The 50-year-old will start at the club in November as its first head of development, ending an 18-year association with Geelong.
Lappin, who won flags with Brisbane as a player in the early 2000s, is considered among the best development coaches in the league.
Tuesday's announcement comes a fortnight after Tasmania revealed former Port Adelaide boss Ken Hinkley as coach.
"I've admired Nigel's work for a long time and I know the impact he'll have on our program," Hinkley said in a club statement.
"His experience, character and commitment to developing talent make him a fantastic addition to our football department."
Tasmania, who will enter the AFL and AFLW in 2028, have a host of draft and list concessions and will have access to some of the nation's most promising 17-year-olds in 2027.
The club joined the VFL and VFLW competitions this season and sit sixth - one spot ahead of the four wildcard positions - in the men's with two rounds to play before the finals.
Lappin, who will remain with Geelong until the end of the season, said it was a rare opportunity to help build a club from the ground up.
"Tasmania has an incredible football history and passion for the game," he said.
"To now have the opportunity to help shape its AFL future is something I feel incredibly privileged to be part of.
"Development isn't just about making better footballers - it's about building better people, creating strong habits and establishing a culture that lasts."
Devils CEO Brendon Gale said Lappin was among the most respected development coaches in Australian football and had demonstrated an exceptional ability to develop players.
"I would also like to thank and acknowledge Geelong Football Club, who have been broad supporters of the establishment of Tasmania Football Club over a sustained period," he said.
"We are confident that Nigel's experience, humility and values make him an outstanding fit for what we're creating."
Lappin played 279 games for the Lions, retiring in 2008.
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