The 32-year-old former Brisbane Lions midfield star will be an addition to the existing coaching panel of Mark Thompson, Ken Hinkley, Brendan McCartney and Brenton Sanderson.
Leigh Tudor will continue with the Cats VFL side.
Lappin retired at the end of the 2008 season after 279 games in Brisbane with both the Bears and the Lions.
He said he was looking forward to relocating to Geelong and working with the stellar team which only lost two games in 2008.
“The club has gone from strength to strength over the years and I have seen, playing against them, how they have developed,” Lappin said.
“I have great respect for the way the club has gone about building its team and am excited to be joining them and working with the players and coaches.
“I can’t wait to get started down there.”
Cats general manager of football operations Neil Balme said Lappin had plenty to offer Geelong.
“Nigel’s record speaks for itself and we are looking forward to his knowledge and teaching ability helping the club to continue to be strong,” Balme said.
Lappin was co-captain of the Lions and won the club’s best and fairest in 2004 when he helped them past the Cats in the preliminary final.
He was also named in the All Australian side for four consecutive years between 2001 and 2004.
