He played in Major League Baseball (MLB) for the San Diego Padres and New York Mets.

In the 1998 Major League Baseball draft, the San Diego Padres selected Lawrence in the 17th round.

After spending the rest of that year at the Rookie League and Class A Short Season levels of the Padres' organization, he played a full season in 1999 with the Class A-Advanced Rancho Cucamonga Quakes, finishing with a 12–8 record and a 3.39 earned run average (ERA).

During the 2000 season, Lawrence split time between the Double-A Mobile BayBears and the Triple-A Las Vegas Stars.

Following the trade to the Nationals, Padres General Manager Kevin Towers was quoted as saying "Brian Lawrence was an effective low cost innings-eater".

On August 2, 2007, Lawrence was called up to the major leagues, and started his first game with the Mets against the Milwaukee Brewers.

On January 19, 2008, the Kansas City Royals signed Lawrence to a minor league contract with an invitation to spring training, he was released from the team on March 27, 2008.

On June 8, the Atlanta Braves bought Lawrence's contract from Camden and assigned him to Triple-A Richmond.

He joined the independent Orange County Flyers of the Golden Baseball League under first-year manager Phil Nevin in 2009.