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 added "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 he had an explosive falling out with head coach Jorge Jesus.
He was suspended for 30 days and fined £215 after he walked out of the squad's training camp on the last international break.
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."
The Portuguese Football Federation praised Ronaldo for his "monumental 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.
Ronaldo is reported to be the highest-paid footballer in the world, with some estimates placing his Al Nassr salary at £488,000 per day.
He holds the all-time record for international appearances and for international goals.
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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 that 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 Frist 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 that 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 that 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 then 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 Frist 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."
Is this the end of MAGA? It is a seismic election result this midterms. The Democrats sweep to a comprehensive victory in both houses of Congress. Parts of the country that have almost always been red are now blue.
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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Sky News understands that Gordon Brothers this week appointed Hanbury Strategy to advise it amid urgent talks aimed at averting Poundland's collapse - which would put 10,500 jobs at risk just weeks before Christmas.
Gordon Brothers, which only bought Poundland last year, is facing demands to explain why a solvent offer for the chain from Martin Property Group was rejected.
The Business, Innovation, Science and Trade select committee has summoned Mark Newton-Jones, the former Mothercare boss who runs Gordon Brothers in Europe to give evidence next Wednesday.
The invitation is said to be under discussion, although Whitehall sources said a response had yet to be received.
Gordon Brothers' decision to hire Hanbury reflects the intensity of the scrutiny it is now confronted by, having met with Jonathan Reynolds, the business secretary
Hanbury, whose partners include former Westminster special advisors, is working with the London & Valley Water consortium which is trying to stitch together a rescue deal for Britain's biggest water utility.
It was also involved in the auction of The Daily Telegraph, which culminated this year following protracted government intervention.
Hanbury declined to comment on its work for Gordon Brothers.
Earlier this week, Sky News revealed details of a letter sent by Gordon Brothers to government officials in which it defended its stewardship of Poundland.
A statement released by Gordon Brothers overnight repeated many of those claims, saying: "We are pursuing all avenues through the sale process to find a solution which protects as many jobs as possible and preserves value.
"Work continues at pace, engaging in active discussions on offers with interested parties.
"We recognise the Poundland business has faced several years of instability.
"When Gordon Brothers acquired the business, it was in distress and required a radical restructure, urgent operational change and significant funding, which we provided to support the company's ability to trade.
"In spite of our efforts and the tremendous efforts of management to deliver a turnaround, the business remains challenged and vulnerable to any potential downturn in future trading.
"Our intent throughout the comprehensive sale process has been to protect as many jobs as possible and preserve value in order to deliver the best available outcome for the people, creditors and local communities who care about this business as much as we do."
Multiple sources have cast doubt on those claims, with Gordon Brothers having rejected a fully funded, solvent offer for the business.
Another party, Xyra Group Holdings, is reported to be interested but is said to lack funding for a deal.
A notice of intention to appoint AlixPartners as administrator, filed a week ago, gives Poundland another week's breathing space from creditors.
Insiders have challenged the need for Poundland to enter any form of insolvency process because of the company's current cash position and trading performance.
Gordon Brothers is understood to have frozen the chain's access to its asset-based lending facility and prevented board executives from accessing the company's bank account.
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".