Wasps director of rugby McGeechan was unveiled as the head coach at a press conference in London.
The 61-year-old Scot masterminded a famous series victory over the Springboks in 1997 and this will be his fourth Lions tour as head coach.
McGeechan has enjoyed a long and successful association with the Lions and has been involved in six previous tours - in 1974 and 1977 as a player, in 2005 an assistant coach and in 1987, 1993 and 1997 as head coach.
Lions chairman Andy Irvine said: "A lions tour is very special - even in the modern game they're as popular as ever.
"Some years ago there was doubt they would even continue but I'm delighted to say they're as popular as ever.
"Many players have said playing for the Lions is the highlight of their career. And we expect 50,000 fans to travel to South Africa.
"The 2005 tour was very disappointing as we lost the Test series 3-0 so it's vital we have the best leadership for to achieve success in South Africa.
"Once Gerald Davies was appointed tour manager all our attentions focused on who would be the best coach. From day one McGeechan was in our thoughts.
"We wanted someone with a special bond with the Lions. We looked elsewhere as well but time and again we kept going back to Ian.
"He's the most successful coach in Lions history."