Mike Ruddock has stepped down as Wales coach because of personal reasons, less than a year after leading them to their first Grand Slam in 27 years.
Ruddock, 46, wanted to see out his current contract until the end of the RBS Six Nations campaign.
But Welsh Rugby Union chief Steve Lewis said that skills coach Scott Johnson will take over with immediate effect.
"This has been a tough decision to make but I have decided to put my family first," said Ruddock in a statement.
"The intense build-up to the World Cup means more time away from my family. That is something I'd like to avoid.
"I have found during my two years as coach that the position is more than a job. That has meant I have spent long periods away from my family."
"Mike Ruddock has empowered the players, which is a big step"
Ruddock's departure was confirmed at a hastily-convened press conference at Cardiff's Millennium Stadium.
The WRU had been in negotiations with Ruddock to extend his deal since last March.
Wales began the defence of their Six Nations crown with a 47-13 loss away to England a fortnight ago, but recovered last weekend with a home 28-18 win over Scotland.
But Lewis said it was in the "best interests of the team" that Ruddock stand down with immediate effect.
Johnson was seemingly set to quit the Wales camp to return to his native Australia, but now there is likely to be a renewed effort to entice him to stay on as head coach.
Former Wales and Llanelli Scarlets hooker Robin McBryde, who retired from playing last year because of injury, will join the Wales set-up as forwards coach.
WRU chairman David Pickering admitted Ruddock's resignation had created a crisis for Wales, but is confident the team is in safe hands with Johnson.
Pickering said: "We handled a crisis. We have a strategy and we've moved forward.
"The inordinate pressure on coaches does affect their family lives, and Mike was a big family man.
"Mike's place in Welsh rugby history is assured. He will go down as a fine ambassador, a wonderful coach, and a fine gentleman."
Meanwhile, Wales and Lions legend Ieuan Evans has praised the contribution of Ruddock during his time at the helm.
Ruddock was in charge for 20 Tests, of which Wales won 13, including the 2005 Grand Slam and a first victory over Australia for 18 years during last year's autumn internationals.
"He has empowered the players, which is a big step - the foundation was laid by Steve Hansen to get the basics right, but Mike Ruddock has given them the freedom to express themselves," Evans told BBC Sport.
"Last season Wales definitely also improved in the tight, so Mike must take credit for that."
Ruddock took over from former coach Hansen in March 2004, surprising many by pipping Llanelli Scarlets coach Gareth Jenkins to the post.