Hammel, who threw five innings in a minor league game Wednesday, is scheduled to start against the Rays' David Price on Tuesday in St. Petersburg, Fla.
"We look it at as one of the five starters. He will be the first guy of the season," manager Buck Showalter said.
Hammel was 8-6 with a 3.43 ERA for the Orioles last season, and pitched Games 1 and 5 in the American League Divisional Series against New York.
"It's an honor," Hammel said. "Very excited. Basically what it means is I get to be the one to get us off on the right foot. I don't take that lightly. Very confident to come out and win there."
Hammel missed much of the second half of last season after surgery on his right knee.
The 30-year-old right-hander has only pitched in three major league games this month because Showalter wanted to avoid using him against American League East rivals.
"I'm very happy to say I made it through healthy," Hammel said. "That was my main concern after last year. It was the first time I dealt with an injury that long and I feel like I've come back stronger from it. I may not have pitched in many Grapefruit League games, but I was able to get the work in I needed to."
The Orioles reassigned their No. 1 draft choice from last year, Kevin Gausman, to minor league camp.