Farrell named British and Irish Lions coach for 2025 tour to Australia
Farrell will work solely with the Lions from December this year until the conclusion of the tour, meaning he would miss Ireland's Six Nations campaign in 2025.
The former England dual-code international recently signed an extension to his contract as Ireland coach till the conclusion of the next World Cup in 2027.
Under Farrell's stewardship, Ireland won a Six Nations Grand Slam last year, the triple crown in 2022 and secured a first ever series win in New Zealand.
Ireland also rose to number one in the world rankings before last year's World Cup.
However, they again failed to make it beyond the quarter-finals of the showpiece event following an agonising quarter-final loss to the All Blacks.
Farrell succeeds Warren Gatland, who has led the Lions on their last three tours to the southern hemisphere dating back to 2013.
He was part of Gatland's coaching team for the 2013 series win in Australia and tied series against New Zealand in 2017.
"It is a tremendous honour and a privilege to be named head coach of The British and Irish Lions," said Farrell.
"I know how special Lions Tours are having been involved in the 2013 and 2017 Tours, so I am delighted to get the chance to lead the team in 2025.
"There is a wealth of talent across Britain and Ireland, and I am looking forward to building a team that can deliver the ultimate goal of success in Australia."
Expectations will be high on Farrell to deliver a series win down under with Australian rugby in crisis.
Eddie Jones quit as the Wallabies coach after just two wins from nine Tests last year that included a group stage exit from the World Cup after defeats to Wales and Fiji.
But Farrell could come up against his former boss Joe Schmidt with the Kiwi linked with taking charge of Australia.
Farrell served as defence coach to Schmidt with Ireland before succeeding him in 2019.