The 32-year-old, who has 16 Grand Tours under his belt, has been a key support rider for Chris Froome at Sky and Alberto Contador at Tinkoff-Saxo in the last few years, and adds experience to BMC's Grand Tour set-up, spearheaded by Richie Porte and Tejay van Garderen.
Roche held the role of road captain for Froome at last year's Tour de France but was left out of the squad this year, and he was first linked with BMC last week. Signings can only be made official as of August 1 and the American squad did not delay in unveiling their first acquisition for next year, though the length of the contract was not disclosed.
"I'm super excited because BMC Racing Team is a team that rides with a lot of the characteristics that I like. They're always up the front, riding with aggression and trying to make an exciting race. I think I'll enjoy the aggressive style of racing," Roche said in a statement.
"Looking ahead to the 2017 season, my main role will be to really support Richie Porte and Tejay van Garderen in their General Classification ambitions, and hopefully I'll have a good go at the Vuelta a España."
Roche, who spent bulk of his career at French teams, will leave Sky after two seasons - the same amount of time he spent at Tinkoff-Saxo before that. The move to BMC will mark his 13th season as a professional.
He was fifth overall at the 2013 Vuelta a España, seventh in 2010, and won a stage there last year, while his best result at the Tour de France was 12th in 2012. This year he won both the road race and the time trial at the Irish national championships and finished the Giro d'Italia, where Sky's plans were derailed by the early abandon of leader Mikel Landa.
"Nicolas Roche is a fantastic addition to BMC Racing Team. Nicolas brings a wealth of experience and is exactly the sort of rider we are looking for to support our Grand Tour ambitions and work for his own personal objectives," said BMC manager Jim Ochowicz. "A lot of our goals are centered around Grand Tours and we felt we needed an additional rider who could bring us experience in that field.