Former dual-code international Farrell, England's defence coach under Stuart Lancaster and now doing that job for Ireland, will fill the role again for the Lions having done it under Gatland during the series victory over Australia in 2013.
Howley, currently leading Wales during Gatland's sabbatical, will again be the backs coach. Borthwick, currently working under Eddie Jones as forwards coach for England, will look after the forwards and bring his lineout expertise to the Lions.
“I said from the outset it was important to have continuity because we need to hit the ground running, given the limited preparation time,” Gatland told a news conference near Dublin on Wednesday as he announced his coaching lineup.
“In Rob and Andy we have guys who understand the Lions concept, have worked together and know how to coach a winning Lions team. It's also important to have some new input.
“Steve has done a great job in shaping the England pack and played a major role in their recent run of success, so I'm looking forward to working with him.”
Gatland confirmed he was also considering an extra specialist coach after media reports on Wednesday suggested Ryan, the Englishman who led Fiji to Olympic gold in Rugby Sevens at this year's Rio de Janeiro Games, could be included.
Ryan spent six years as England Sevens coach before taking over Fiji and transforming them from a side of brilliant but erratic performances into the dominant force in the Sevens game, culminating in their Rio triumph when they beat Britain in the final to win their country's first ever Olympic medal.
Ryan stood down from the role after the Olympics and is currently working as a consultant.
“I think over the next couple of months I want to add some specialist people in the coaching set-up,” New Zealander Gatland said. “There's no rush, it's just a case of making sure I speak to the right people.”
Gatland, however, declined to confirm that Ryan was among them and laughed off some of the speculation.
“Some of the names have been fantastic,” he said. “I haven't heard of some of them.”
The Lions will tour New Zealand next June and July, playing three Tests and seeking only their second series win in the country after their 1971 triumph. They were hammered 3-0 in their last tour their in 2005 under Clive Woodward.
Original source: Gatland names Lions backroom staff