He made his debut for the Atlanta Braves in 2003, when he had a 4.00 ERA over 29 starts. At the end of his rookie season, he was selected to the Baseball Digest All-Star Rookie team. He got off to an excellent start in 2004 with a 2.39 ERA in the first nine starts, before he suffered a shoulder injury, initially thought minor, but which eventually sidelined him for the rest of the season, except for one September relief appearance.
In 2005, Ramírez finished with a record of 11-9 and an ERA of 4.63. He pitched over 200 innings for the first time in his career. He remained in the Braves' rotation in 2006 as the number 3 starter.
On December 6, 2006, the Atlanta Braves traded Ramírez to the Seattle Mariners for right-handed relief pitcher, Rafael Soriano.
In his lone season with Seattle, he had an ERA of 7.16 in 20 starts despite having a record of 8-7.
On March 12, 2008, Ramírez was released by the Mariners.
On May 21, he signed a minor league deal with the Kansas City Royals. He pitched in 15 games for the Royals out of the bullpen, sporting a 2.59 ERA.
On August 9, 2008, Ramírez was traded to the Chicago White Sox for outfielder Paulo Orlando.
On December 11, 2008, Ramírez signed a one-year deal with the Kansas City Royals On June 6, he was designated for assignment by the Royals.
After his release from Kansas City, on June 15, 2009, Ramírez signed a minor league deal with the Washington Nationals.
On February 1, 2010, Ramírez signed a minor league contract with the San Francisco Giants.
On March 11, 2011, Ramírez signed a minor league deal with the Los Angeles Angels of Anaheim.
On July 20, 2011, the Angels purchased Ramírez's contract. He worked out of the bullpen once again but was not effective, allowing 16 hits in 9 innings and having an ERA over 5.00 in the process. The Angels released him after the season.
On February 20, 2012, Ramírez signed with Kia Tigers of the Korea Baseball Organization.
On August 17, 2012, Ramirez signed with the Chicago Cubs after being released by the Kia Tigers.
On January 18, 2013, Ramirez was part of the Mexico roster in the World Baseball Classic.
On June 14, 2013, Ramirez signed with the Lancaster Barnstormers.
On March 10, 2014, the Braves announced that Ramirez would be joining their coaching staff as a coaching assistant. He was brought on to assist the coaching staff with on-field duties prior to games and manage the Braves instant replay protocol from an off-field location during games.
On March 5, 2016, Ramirez signed with the Toros de Tijuana of the Mexican Baseball League.