The 25-year-old was unveiled by the Ligue 1 side on Monday after leaving Lorient after four years and 195 league appearances.
Monnet-Pacquet claimed he has opted for Saint-Etienne as they are a club that can help him push on from a season that saw him score four goals in 36 league matches.
"I wanted to join an ambitious club playing at the top of the table," he told the club's official website.
"Saint-Etienne perfectly meets my expectations.
"The team is on a good momentum for several seasons. The talks with the coach (Christophe Gaultier) motivated me.
"I'm excited about playing at Stade Geoffroy-Guichard and taste the European Cup again.
"It is here that I can continue to new levels."
Gaultier believes Saint-Etienne, who finished fourth last season, have acquired a player who will help them continue to grow as they prepare to return to European competition.
"Kevin is a player that we have followed for a long time," the coach said.
"I wanted to have a player like him in the squad.
"He is a very good team player."
