Long struggled with inconsistency in his five years in the Mets minor league system, but he earned a call-up in early April 1999 and played in three games, failing to get a hit in three pinch-hit appearances, before being sent back down to Triple-A Norfolk.

On July 23, 1999, the Mets traded him and minor leaguer Leo Vasquez to the Oakland Athletics for former All-Star pitcher Kenny Rogers.

In 2000, after a fast start while playing in Triple-A, the Athletics called up Long, and he spent the rest of the season with the major league team.

On November 26, 2003, the Athletics traded him and All-Star catcher Ramón Hernández to the San Diego Padres for outfielder Mark Kotsay.

In the 2005 offseason, Long became a free agent, and eventually signed a minor league contract with the Cincinnati Reds, however he failed to make the major league roster out of spring training, and struggled to a .229 batting average in 15 games with the Reds Triple-A affiliate, the Louisville Bats and was released by Cincinnati on May 5, 2006.