Chris Coleman has left his job with Wales to take over at Championship club Sunderland.
Coleman will succeed Simon Grayson, who was sacked after 18 games in charge.
The Football Association of Wales (FAW) confirmed: “Regretfully, Chris Coleman has resigned from his position with immediate effect.”
Ex-defender Coleman, 47, succeeded the late Gary Speed in 2012 and guided them to an historic appearance at Euro 2016, where they reached the semi-finals.
Disappointment followed as Wales failed to reach the 2018 World Cup finals in Russia.
Coleman’s assistant, Kit Symons, has also left his role of Wales coach.
FAW ‘extremely disappointed’ by Coleman departure
FAW chief executive Jonathan Ford said: “We are extremely disappointed to see Chris’ tenure as Wales manager come to an end.
“The FAW and Wales as a nation will be eternally grateful for the job he has done over the last six years as national team manager, from travelling the length and breadth of Wales outside of the media spotlight to talk to players and supporters, to guiding us to the semi-finals of the European Championships.
“We wish Chris the very best of luck for the future as he returns to club management, a desire for which he has always been honest and open about.”
After Wales’ qualifying campaign for the 2018 tournament ended in defeat by the Republic of Ireland, Coleman’s last two games in charge were a loss to France and home draw against Panama in November, 2017.
Negotiations between Coleman and the FAW continued after the game against the Central Americans.
Those talks ended with Coleman leaving. He had often spoken about hoping to return to the day-to-day demands of club management amid a career that has included being in charge of Fulham in the Premier League.
‘I’m gutted, really disappointed’ – Gabbidon
Ex-Wales defender Danny Gabbidon told BBC Sport Wales: “I’m gutted, really disappointed. I know all the fans will be, the players will be as well.
“I know how much they thought of the manager – he was more than just a manager.
“There was a kind of player relationship between the squad and the manager so they’ll be gutted hearing that news as well.”
Coleman’s reign began with Wales 48th in Fifa’s world rankings and it ends with them in 14th place.
He will take over at Sunderland, who are bottom of the Championship with one win, seven draws and eight defeats so far this season.
Sunderland are aiming to confirm a deal with Coleman by Sunday.
There is an expectation at the Stadium of Light he will be in charge for their away game against Aston Villa on Tuesday night.
Despite speculation over Northern Ireland boss Michael O’Neill, Coleman was the club’s number one target and no offers were made to other candidates.
Coleman wanted the FAW to employ head of performance Ryland Morgans and psychologist Ian Mitchell on full-time contracts.
The FAW also offered to spend £500,000 on upgrading training facilities.