Means provided the update on social media after he was put on the 10-day injured list on April 15 and later transferred to 60-day IL because of a sprained elbow.
"After multiple MRI's it's confirmed that I need Tommy John surgery," Means wrote. "I'm obviously disappointed, but more motivated than ever. In the meantime, I'm looking forward to watching what this team can do this year."
An All-Star in 2019, Means was 0-0 in two starts this season, giving up three runs in eight innings.
In May, Means pitched a no-hitter against Seattle. He nearly missed a perfect game as the only Mariners runner to reach came on a wild pitch on strike three.
Means was 6-9 with a 3.62 ERA last season, leading a staff that had the worst ERA in the majors.
Orioles manager Brandon Hyde said before Saturday night's game against the Los Angeles Angels that losing Means is a tough blow to one of the majors' youngest rotations.
"John's a big part of our pitching staff. Not only what he brings on the mound, but also the leadership in our clubhouse," Hyde said.
Even with Means' injury, the Orioles are off to a strong start on the mound. They entered Saturday with a 2.80 ERA, which is tied for second in the American League. It is the first time since 1992 that they have pitched to a sub-3.00 ERA through their first 14 games.
Baltimore's starters have not allowed more than two earned runs in 11 consecutive games, pitching to a 1.69 ERA during that span.
"A lot of guys are confident and hungry," Hyde said. "Outside of Jordan [Lyles], guys don't have a ton of major league experience. They want to stick in the big leagues, and they want to contribute. They're off to a good start and let's see it continue."
The Associated Press contributed to this report.