In a social media post, the 41-year-old said: "Today, the time has come to pass it on to the future. It was not an easy decision."
He said "thank you for these 23 years" and "Portugal will always be a part of me".
Ronaldo said he would "hand back the number 7 shirt" after the November international break.
The decision to bring his glittering football career to a close comes after a falling out with head coach Jorge Jesus.
Ronaldo was suspended for 30 days and fined £215 after he walked out of the squad's training camp on the last international break. He later apologised and cited broken promises from Jesus as the reason for his departure.
It was a sad ending to a lauded career that began more than two decades ago before Euro 2004 and saw him make 234 appearances for Portugal and score 146 goals.
Adding that it had not been an "easy decision", Ronaldo said: "If I ever made you happy, if one of my goals ever made you hug someone, forget a worry or feel proud of our country, then it was all worth it."
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The Portuguese Football Federation praised Ronaldo for a career during which he "carried the nation on his shoulders, shattered records, and led the team to achieve moments that will remain forever etched in the history of our national football".
"Every drop of sweat, every decisive goal, and every time he wore the captain's armband with honour on the pitch served as a reflection of his unconditional love for our jersey," the federation said.
"His commitment and his legacy transcend the boundaries of the playing field."
The federation said a "fitting tribute" to Ronaldo's "immense career" would be organised in the future.
This statement draws a line under speculation among football fans and the Portuguese media that a September match against Wales had been an unofficial farewell for Ronaldo.
He is reported to be the highest-paid footballer in the world - with some estimates placing his Al Nassr salary at £488,000 per day - and holds the all-time record for international appearances and for international goals.
Ronaldo and Argentina's Lionel Messi are the only players to feature at six global tournaments.
The media regulator opened an investigation into the dating show in July following a "fairness and privacy" complaint.
At the time, Ofcom said it was investigating an unspecified complaint against the reality TV show.
The reality series, in which single people are matched and 'married' to complete strangers, was investigated by the BBC's Panorama earlier this year.
Its report, broadcast in May, included allegations by two women that they had been raped during production of the show. Another woman alleged a non-consensual sexual act.
All three said the Channel 4 show, made by production company CPL, did not do enough to protect them.
All three men deny the claims.
Channel 4 chief executive Priya Dogra confirmed season six of the show, which was filmed earlier this year, will not be broadcast.
The review was commissioned by Ms Dogra earlier this year following the allegations made on Panorama.
The review had two elements:
- Law firm Clyde & Co examined the welfare protocols in place at the time the claims were initially raised, and how Channel 4 and production company CPL handled them.
- Former BBC One controller Lorraine Heggessey examined if any changes should be made to current protocols for Married at First Sight UK to further strengthen contributor welfare.
Channel 4 said neither element of the review "sought to adjudicate" on the serious allegations of wrongdoing highlighted by Panorama, which it said "remain a matter for the relevant authorities".
Outcome of the review
The Clyde & Co review, which reviewed 31,172 documents and 20 hours of broadcast and unbroadcast footage, found that Channel 4 and production company CPL's welfare protocols were compliant with the Ofcom Broadcasting Code.
It also found there was no breach of the code in regard to the handling of issues raised.
However, the review noted there were isolated incidents where the welfare framework was not fully implemented.
It cited an instance when some contributors contravened the code of conduct relating to "prohibited substances" but were given a first and final warning rather than being removed from the programme.
Meanwhile, Ms Heggessey's report cited that some elements of the show could "implicitly put pressure on contributors to be intimate" and contributors could "become dependent on production and lose touch with reality", which could affect their "decision-making".
It also recommended that the "frequency" with which couples were asked about the physical side of their relationship should be reviewed and that certain events, such as Intimacy Week and Partner Swap Week, should be discontinued.
The review also said other changes to consider included changing the leave/ stay mechanism so that if one person in a couple chose to leave the show, they could do so, rather than be forced to continue.
On the show, couples can choose whether to "stay or leave" during weekly Commitment Ceremonies, however, if one chooses to leave but another asks to stay, both must remain for another week.
Despite that, her review found that welfare protocols for the show were "extensive, extremely thorough and of a high standard".
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The review said that with enhancements to the existing contributor welfare framework and adjustments to the format, it would be reasonable to continue to produce future seasons of the show.
The broadcaster said that "taken together with the maturity of the programme", Ms Dogra determined the "right course was to bring Married At First Sight UK on Channel 4 to an end".
She said: "Welfare across all our programmes is a primary concern."
"Whilst the review praised the welfare protocols in place and made no findings that Channel 4 breached the Ofcom Code or that the format is inherently unsafe, I have to consider when is the right time for Channel 4 to move on from a format."
Channel 4 said the show's budget would be "reinvested in distinctive new programming".
A statement from CPL said: "CPL understands Channel 4's decision to bring Married At First Sight to an end on the channel."
"The independent reviews gave CPL the opportunity to discuss in depth the welfare processes already in place and that the Heggessey review found that 'the welfare protocols for Married At First Sight UK were extensive, extremely thorough and of a high standard from which other productions in the industry have learnt'.
"CPL has always put contributor welfare at the heart of its programme making and will continue to do so."
Dame Caroline Dinenage, chairwoman of the digital, culture, media and sport committee, said the decision made sense given the findings of the review and seriousness of the allegations.
"Reality TV contestants have often been treated as a commodity, with duty of care a slogan rather than a genuine principle. Everyone involved in producing and regulating reality TV must now learn and act," she added.
Prosecutors say the man, who is in his 60s and from Stockport, exposed the woman to a cocktail of potentially "fatal" drugs without her knowledge.
He filmed the abuse, amassing more than a million images, which he shared online and allegedly invited men to the family home to rape and sexually assault his wife, while she was unconscious, from at least 2023.
The husband, who cannot be named to protect the identity of the woman - has admitted 62 offences between 2004 and 2025.
He will give evidence for the prosecution against nine other men on trial at Manchester Minshull Street Crown Court, where they deny a variety of sexual offences against her.
"He says he wants to tell the truth," prosecutor Louise Oakley KC told the jury, explaining he wants his wife and their family "to know what happened".
"He is not doing it to get a reduced sentence. He fully expects to die in prison for what he has done."
The jury was shown messages his wife sent to a friend after she was drugged and allegedly attacked by her husband and two other men - Mohammed Sabir, 28, and Robert Stewart, 70 - in the same night in September last year.
She said she had "only just woken up" shortly before 1.30pm feeling "wobbly, woozy and a bit weird" and asked: "What's wrong with me?"
Stewart later sent the husband a message telling him to "delete all images" because of "the guy in France", which Ms Oakley said was a reference to Gisele Pelicot.
"His own comparison of what happened to her and his conduct, you may think, perhaps sums up this whole case from start to finish," she said.
Men continued to contact the husband to ask him to "abuse" his wife even after he was arrested in October last year, the jury was told.
Cocktail of drugs found in hair sample
The court previously heard the only medication the woman took regularly were multi-vitamins and tablets for high blood pressure, cholesterol and heartburn prescribed by her GP.
But an 8cm hair sample was analysed by a French forensic toxicologist, which could represent eight months of drug exposure - assuming hair growth of 1cm a month - but was likely an "underestimate".
It revealed a cocktail of drugs or medications, including morphine, ketamine and cocaine, as well as other sedatives and anti-depressants - none of which she had been prescribed.
Ms Oakley said when one of the sedatives is mixed with alcohol, "the risk of severe sedation increases and could be fatal".
The court heard how the husband researched "date rape drugs" online and crushed up tablets to give to his wife in food and drink - but the medication turned wine cloudy and made her curry taste bitter.
Police also seized pipettes from the bedroom drawer, which had traces of the medication he used to drug her, the jury was told.
The husband has pleaded guilty to all of the charges he faced, including multiple counts of rape and administering substances with intent to stupefy his wife, and will give evidence for the prosecution.
Kitchen firm sales rep David Graves, 60, of Ilkeston, Derbyshire, and mechanic Daniel Rayner, 42, from Whitstable, Kent, deny conspiracy to rape, conspiracy to assault by penetration and conspiracy to administer a substance with intent.
Stewart, of Stockport, denies rape, conspiracy to rape and conspiracy to administer a substance with intent, while Sabir, of Stockport, denies rape and conspiracy to rape.
Taxi driver Philip Wild, 59, of Stockport, has pleaded not guilty to sexual assault, attempted rape, assault by penetration and conspiracy to rape.
Industrial cleaning firm worker Alan Keelan, 42, from Manchester, denies attempted rape and assault by penetration, while building supplies worker Jordan Wallace, 31, from Manchester, denies rape and attempted rape.
Sheet metal worker Richard Townsend, 38, from Greater Manchester, denies assault by penetration; and senior paramedic Jonathan Kirk, 43, of Stockport, denies rape and conspiracy to rape.
Four other men, Graham Brougham, 74, from Northwich, Cheshire; Sean Peers, 38, from Stockport; Keith Fotheringham, 59, from Dundee, and Karl Lindsay, 56, from Taunton, Somerset, have admitted their sexual offending.
The trial continues.
A consultation launched on Thursday will set out proposed new national standards and powers for local leaders to keep pavements clear and make journeys safer.
More radical options are also being explored, such as allowing local leaders to set fees and insurance requirements for operators.
Shared e-bikes, such as Lime, Voi, Beryl, Dott, Forest and Bolt, are an increasingly popular way to get around, with dockless e-bikes first arriving in the UK in 2018.
Prime Minister Andy Burnham said while e-bikes can make getting around easier, they can be "a real frustration" when they block pavements or are used irresponsibly.
Proposed measures include a parking and fleet management plan, setting out fleet sizes and operating areas to prevent overcrowding on pavements.
Action for antisocial and illegal behaviour is also being planned to prevent users from riding shared cycles drunk, underage, or on pavements.
The government also plans to set out clear consequences for those breaking these rules, such as fines.
Operators could also face requirements to share data with local authorities to improve enforcement and journey planning.
Insurance requirements for operators that would allow people to claim compensation if hit by someone on a shared cycle are also a possibility.
Transport Secretary Heidi Alexander said shared e-bike schemes had "revolutionised" how people travel in towns and cities.
However, she stressed the need to "make sure they work with, not against, the communities where they operate".
Agustin Guilisasti, founder and CEO of Forest, a London-based shared e-bike firm, said the city needed national standards and a coherent, well-regulated system.
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The government hopes the plans will provide greater certainty on where and how cycle schemes run, putting an end to the patchwork of rules for operating in different areas.
Eleanor Briggs, head of policy, public affairs and campaigns at Guide Dogs, welcomed the consultation.
"For people with sight loss, badly parked rental e-bikes are a barrier to independent travel, blocking pavements, creating unexpected obstacles and making it harder to navigate safely," she said.
She added that the charity "frequently hears from people with a vision impairment about irresponsible and antisocial use of e-bikes on pavements, putting pedestrians at risk".
Are these election results the end of MAGA?
The Democrats this week swept to a comprehensive victory in both houses of Congress.
Parts of the country that have almost always been red are now blue.
But what does this mean for Donald Trump? Will it be a reckoning for him and his agenda? And how has he reacted?
We go through the results - live from Michigan, Texas and Washington DC.
Want to hear our US correspondent James Matthews talk about his confrontation with Michigan's Abdul El-Sayed? Scroll to 18 minutes and you'll get his thoughts.
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