Lerew, a graduate of Northern York High School in Dillsburg, Pennsylvania, was drafted by the Atlanta Braves in the 11th round of the 2001 Major League Baseball Draft. After four seasons in the Braves' minor league system, he debuted on Sept. 4, 2005, in a home game against the Cincinnati Reds. In the 2005 season, Lerew recorded no wins, no losses, 5 strikeouts, and a 5.62 ERA in 7 games, all of which were relief outings.
On Feb. 23, 2006, the Braves signed Lerew to a one-year deal. A month later, on Febr. 23, he was optioned to the Triple-A Richmond Braves. With Richmond, Lerew compiled a 3-5 record with a 7.48 ERA and 69 strikeouts in 16 games, 15 of which he started.
The Braves called up Lerew from Richmond on Sept. 1, 2006. He made his '06 debut the next day, making a relief appearance in the fifth inning. Lerew pitched 2 innings, allowing 5 runs and striking out 1 batter. He was sent back down to the Richmond Braves on September 4, having appeared in only 1 game.
On May 8, 2007, Lerew made his first big-league start for Atlanta when he was called up from Richmond yet again, this time to replace Mark Redman in a game against the San Diego Padres. He was later sent down to Richmond again.
On June 20, 2007, Lerew underwent season-ending Tommy John surgery and was placed on the 60-day disabled list. He recovered from surgery in Southern Florida, at the Braves extended spring training site. Once recovered, he spent the rest of 2008 pitching for the Gulf Coast Braves and with Triple-A Richmond.
Lerew spent the 2009 minor league season with the Double-A Northwest Arkansas Naturals. He was called up to the Royals as a September callup, making his Royals debut on Sept. 24, 2009.
On June 16, 2010, Lerew was called up from the Triple-A Omaha Royals to the Kansas City Royals to replace Luke Hochevar, who went on the DL with a sprained elbow. He earned his first career major league win on June 28 of that year over the Chicago White Sox.