The 61-year-old New Zealander said: “I would like to thank the WRU board for the faith shown in me after a tough campaign throughout 2024 and affording me the time and resources to try to turn things around for this 2025 tournament.
“We have worked hard, we have a talented young squad that is developing and have been desperate to turn potential into results but now is the right time for a change.”
Wales, who finished bottom of the Six Nations last year with five defeats, are on course for another embarrassing whitewash after a 22-15 loss in Italy at the weekend.
They face a daunting task against two-time defending champions Ireland on February 22 in Cardiff before a trip to Scotland and a home fixture against England.
Gatland’s position came under formal review after the November internationals, which featured defeats against Fiji, Australia and South Africa.
Speaking at the time, Tierney said she would “make no secret of the fact that his position was on the line as we undertook our review”.
Wales were hammered 43-0 by France in their opening game of the Six Nations before their defeat on Saturday, which was their first loss in Rome for 18 years.
Rankings slump
The proud rugby nation have slumped to a new low of 12th in the world rankings, below Georgia.
Gatland replaced compatriot Wayne Pivac in December 2022, returning to a job where he had enjoyed marked success in his first spell in charge, from 2007 to 2019.
That yielded four Six Nations titles - including three Grand Slams - and two appearances in World Cup semifinals.
They briefly occupied top spot in the world rankings.
Gatland’s team registered just one win in the 2023 Six Nations, but the former British and Irish Lions coach led them to the quarter-finals of the World Cup in France later that year.
Wales have not won a Test match since beating Georgia in the pool stages of that tournament, with defeat to Argentina in the quarter-finals marking the start of their miserable run.
Gatland had to work against the backdrop of a threatened strike by Wales players early in his second stint, linked to a deep financial crisis in the Welsh game.
He has also had to cope with the retirements of a host of experienced players including Alun Wyn Jones, Justin Tipuric, Rhys Webb, Dan Biggar, Josh Navidi, Leigh Halfpenny and George North.
Tierney said the WRU aimed to have a permanent appointment in place before the two-Test tour to Japan later this year “with all options open”.
