Farrell, who left the Men in Black to join England at the end of 2011, will work with acting Head Coach of Wales, Rob Howley and fellow England Assistant Coach, Graham Rowntree.
All three will help Warren Gatland to form the core of the coaching team, with all but Farrell making their second successive Lions Tour.
Warren Gatland told the official website: “I am delighted with today’s appointments and confident that Rob, Graham, Andy and myself can come together quickly to face one of the hardest rugby challenges.
"Lions Tours are unique as we have to mold together players from four different countries in an incredibly short space of time.
“We have no illusion as to the hard work required but we have spoken of the challenges and truly believe that as a coaching team we can provide the players with the support and environment needed for victory in Australia.
"We will also discuss over the coming weeks the requirement for any further technical assistance.”
England Head Coach Stuart Lancaster moved to congratulate both Farrell and Rowntree on their appointments.
“I am delighted for Andy and Graham," he said.
"They have worked hard to achieve this honour and it is a credit to them, the England team and the RFU that they have been asked to coach the best players from the Home Unions.
"They, along with Mike Catt, are fundamental to what we are trying to build with England and I know they will return from Australia with new skills which will benefit us. We wish them and the Lions every success.”