Warren Gatland, who managed the previous three visits in 2021, 2017 and 2013, will be replaced by the Ireland manager.
A contract extension with the IRFU until the end of the 2027 Rugby World Cup was recently signed by Farrell, who assisted Gatland as an assistant coach on the 2013 and 2017 tours. The agreement included a clause allowing Farrell to take a leave of absence from his position with Ireland for the 2025 Six Nations in order to prepare for the tour of Australia.
"It is a tremendous honour and a privilege to be named head coach of The British & Irish Lions," Farrell stated.
"Having participated in the 2013 and 2017 Tours, I am aware of the unique nature of Lions Tours, thus I am thrilled to have the opportunity to lead the team in 2025.
"Britain and Ireland have a plethora of potential, and I am excited to assemble a team that can achieve Australia's ultimate goal of success. I express my gratitude to the Irish Rugby Football Union for their invaluable support in granting me the privilege of accepting this esteemed opportunity."
Farrell was named head coach by a panel of former players and coaches including Brian O'Driscoll, Ian McGeechan, Nigel Redman, as well as Lions chairperson Ieuan Evans and CEO Ben Calveley.
After Ireland defeated New Zealand in a Test series in 2022 and completed a Six Nations Grand Slam in 2023, his appointment had been anticipated for some time.
Additionally, despite Ireland's elimination from the Rugby World Cup following a quarterfinal loss to New Zealand, their performance in 2023 earned him the World Rugby Awards Coach of the Year title.
His first game as Lions leader will take place in Dublin, with the team hosting Argentina at the Aviva Stadium on 20 June next year ahead of their departure for Australia, where they will play nine more matches.
The Lions will play the Western Force in their first match in Australia. They will also play the Queensland Reds, NSW Waratahs, ACT Brumbies, Melbourne Rebels, and an Anzac XV selection.
The Lions and Wallabies are scheduled to play their first Test on July 19 in Brisbane. There will then be follow-up Tests in Melbourne on July 26 and Sydney on August 2.