The 27-year-old right-hander will be the first Orioles starter to pitch three consecutive Opening Days since Mike Mussina did it from 1998-2000.
"It says something about his dependability from a postup standpoint," Showalter said. "Chris has been a durable performer."
Tillman is a year removed from his best season in '14. Tillman went 13-6 that year, with a 3.34 ERA in 34 starts, and he was a late addition to the American League All-Star team.
"It fit best for this outing and what it means down the road," Showalter said of the selection, adding that Ubaldo Jimenez and Yovani Gallardo were both under consideration.
"I think if Yovani had been with us from the first day, it might have been more of a factor."
In seven Major League seasons, Tillman is 56-42 with a 4.20 ERA in 149 games, all starts. He is 0-4 with a 4.82 ERA in six career games against the Twins and 27-21 with a 3.93 ERA in 75 games at Camden Yards.
Jimenez and Gallardo are expected to start following Tillman, with Showalter confirming that Kevin Gausman will begin the season on the disabled list with right shoulder tendinitis. Given the team's schedule, the Orioles won't need a fifth starter until April 10, and Gausman is a candidate to start that game.
Brittany Ghiroli is a reporter for MLB.com. Read her blog, Britt's Bird Watch, follow her on Facebook and Twitter @britt_ghiroli, and listen to her podcast. This story was not subject to the approval of Major League Baseball or its clubs.