The Lille OSC forward has signed a bumper five-year deal with the Billy Goats, while the transfer fee remains undisclosed.
At the foot of their announcement, Köln added this in bold: "1. FC Köln has taken the necessary medical steps to complete the signing of Sehrou Guirassy."
Plenty of potential
Guirassy arrives in Köln with eight goals in 16 games for Auxerre at the end of last season, where he was loaned out to by Lille.
He joined the northern France giants back in 2015 from Stade Laval, as he worked his way through the French footballing pyramid.
The 20-year-old featured in 13 matches for Lille but failed to get the game time he needed to fully excel, but showed just why he is so talented at Auxerre.
Guirassy hit the headlines in the summer for a string of impressive performances at the Toulon Tournament, where he scored three goals and finished as second top goalscorer.
The Frenchman becomes their fourth summer signing, after Marco Höger, Konstantin Rausch and Artjoms Rudnevs all joined the club.
Stöger has his say
Head coach, Peter Stöger gave his thoughts on the move to the club website. He said: “Sehrou Guirassy is a direct forward with an eye for goal and a clinical finish."
The Austrian also praised his versatility, adding: "Guirassy is a central striker, but he can also play on the wings."
Stöger went on to commend Guirassy's performances for France, "His appearances for the youth sides of the French national team are proof that he has been well trained."
He concluded, "We want to develop this young player. We believe in his potential."