Colapinto, 23, joined Alpine as a reserve last season, replacing dropped Australian Jack Doohan after six rounds.
This year he has scored in six of 12 rounds so far, contributing 19 of the fifth-placed team's 63 points.
Gasly has a contract until the end of the 2028 season.
"We have seen Franco truly grow and mature into a great driver this year," said team boss Flavio Briatore in a statement.
"His results in Miami and Montreal especially confirmed what I already knew: Franco belongs in Formula 1 and he belongs at this team."
Colapinto, whose best result this season is a sixth place in Canada, said he felt settled at Alpine and the team had made significant progress.
"Our long-term goals are obvious - to compete and win - and I am grateful to the team, Flavio and (managing director) Steve (Nielsen), for the trust placed in me to be one of its drivers going into the future," he said.
The next race is the Italian Grand Prix at Monza on September 6.