NEW YORK (CNN/Money) - Former Viacom president Mel Karmazin is joining Sirius Satellite Radio as chief executive officer.

A Sirius spokesman confirmed the hiring Thursday, after the story was first reported on AdAge.com

Sirius (down $0.23 to $4.72, Research) shares soared 22.6 percent on the news after the bell to trade at $5.69.

Karmazin's name has been mentioned in connection with Sirius ever since the satellite radio company signed radio personality Howard Stern to a five-year, $500 million deal last month.

Karmazin has worked closely with Stern in the past and has often defended the shock jock.

Although Stern is under contract with Viacom's Infinity Radio until 2006, he has been laying the groundwork for his shift into satellite radio. Tuesday Stern handed out hundreds of free Sirius radios, and vouchers for thousands more, to fans in Manhattan's Union Square.

Karmazin was a key player in the successful integration of CBS Corp. into Viacom in 2000, as well as in the acquisition of his Infinity Broadcasting by CBS in 1996.

Since leaving Viacom in May, Karmazin has been mentioned as a possible successor to Walt Disney's (Research) Michael Eisner, although just last week Karmazin said his future involved linking up with an investment company, joining a high-growth company or doing nothing.