The 31-year-old Roethlisberger, who will miss next week's minicamp, is expected to return when Pittsburgh opens training camp in July.
"This surgery will have no long-term effects on his health," Tomlin said.
Doctors operated on Roethlisberger's right meniscus, a source familiar with the situation told ESPN NFL Insider Adam Schefter. It was the same procedure that was performed in 2005 on his left knee, which has been injury-free since. Roethlisberger missed four games that season but came back to lead the Steelers to their fifth Super Bowl title.
Roethlisberger could have played through his current injury, but team doctors urged him to get his knee repaired, the source said.
Roethlisberger had been a full participant during organized team activities but was concerned enough about the knee that he brought it to the team's attention. Advisors suggested he have the surgery now to give him a clean bill of health when the season begins.
The two-time Super Bowl winner has dealt with a series of issues the last several years. He missed one game and was limited in several others with a right ankle injury in 2011 and sat out three games in 2012 with a cracked rib that was in danger of puncturing his aorta. He was in the middle of a career year at the time but wasn't the same when he came back as the Steelers fell to 8-8 and missed the playoffs.
Pittsburgh revamped the backup quarterback position during the offseason, letting Byron Leftwich and Charlie Batch go in free agency. The Steelers signed Pittsburgh native Bruce Gradkowski in March and drafted record-setting Oklahoma quarterback Landry Jones in the fourth round of the NFL draft. John Parker Wilson is also in the mix.
Gradkowski will work with the first team in Roethlisberger's place when the Steelers wrap up OTAs with a rare practice at Heinz Field on Thursday.
ESPN's Adam Schefter and Ed Werder and The Associated Press contributed to this story.