The Sharks, who entered the day tied for fifth in the Western Conference, sent left wing Ville Nieminen, college forward Jay Barriball and a first-round pick in this year's draft to the Blues.
Guerin, arguably the biggest name on the trading block, led the Blues this season with 28 goals and 47 points. The 14-year veteran waived his no-trade clause to leave the rebuilding Blues for the Sharks, who could contend for a Stanley Cup championship.
"I'm thrilled," Guerin said. "This is one of those teams that was on my radar. I am very happy to be going there.
"You have certain expectations and places that you want to go. ... When it was presented to me, it was a no-brainer."