The Raiders sent a late-round pick in the 2014 Draft to the Texans for the 32-year-old to join the club and likely become their starter for the next campaign.
Olson told reporters: "Obviously he's had a tremendous amount of experience. He's at an age right now where most quarterbacks are in their prime.
"We feel like he's got a lot of football ahead of him. He's a proven winner. We weren't going to let last season deter us from the player and the track record that he has shown over his career.
"Like I said, he was our number one target from day one. It was just a matter of getting the deal done. Feel fortunate to have the player."