Seattle Mariners On September 1, 2007, Ramírez officially signed with Seattle Mariners. Ramírez began his
professional baseball career in 2008 with the
rookie-level VSL Mariners of the
Venezuelan Summer League. That season, he compiled a 4–1
record with a 2.86
earned run average (ERA), one
complete game, and 46
strikeouts in 13 games, 11
starts. In 2009, Ramírez continued playing with the VSL Mariners. Before the season, the Seattle Mariners minor league director
Pedro Grifol compared Ramírez to
Major League Baseball pitcher
Doug Fister. After the season, the Seattle Mariners named Ramírez as the pitcher of the year in their minor league organization. He participated in the Mariners instructional league in
Arizona after the 2009 season. He was assigned to the
Single-A Clinton LumberKings in early-April. At the end of the year, Erasmo was awarded in Nicaragua Athlete of the Year by the ACDN (Nicaraguan Association of Sport Journalists) over
Everth Cabrera. In 2013, Ramírez was going to join the Mariners starting roster before the start of the regular season before injuring his triceps. He eventually spent time in
Triple–A before making his debut of the season with the Mariners on July 11 against the
Boston Red Sox, but allowed seven runs in 4 2/3 innings. The following day, Ramírez was sent down to the
Everett AquaSox in order to allow him to stay on a regular rotation during the Major League All-Star break, and started July 17's game against the
Vancouver Canadians, giving up two runs on six hits while striking out ten in 5 1/3 innings as the AquaSox won 7-6.
Tampa Bay Rays On March 31, 2015, Ramírez was traded to the
Tampa Bay Rays for
Mike Montgomery. Ramírez struggled in his first month with the Rays, posting an 0-1 record with a 12.71 ERA. But, when he came back in mid-May from the
Durham Bulls he was better for the rotation and team, putting up great numbers for the rest of the season. On September 14 against the
New York Yankees he went 7 hitless innings. Ramírez finished the season 11-5 with a 3.75
ERA in 163 innings pitched. In 2016, Ramírez made a more permanent switch to the bullpen, specifically in long relief situations. Ramírez ended the season making appearances in 64 games, throwing 90 innings posting a 3.77 ERA. In 2017, Ramírez started as an important reliever out of the bullpen, but when struggling youngster
Blake Snell was demoted, Ramírez was put in the starting rotation. On May 28, Ramírez was forced to come in and get a save in a fifteen inning affair with the
Minnesota Twins. On May 29, Ramírez became the first pitcher since
Dennis Martinez, Ramírez's childhood idol, to start the next game after receiving a save.
Seattle Mariners (second stint) On July 28, 2017, the Rays traded Ramírez back to the
Seattle Mariners for
Steve Cishek. On August 23, Ramírez went 2-for-3 at the plate in a game against the
Atlanta Braves, recording his first MLB hit and RBI. On May 1, 2018, he was placed on the disabled list. He ended the season sporting a career worst 6.50 ERA in 10 starts. Nevertheless, on October 29, 2018, Ramírez was selected to play in the
2018 MLB Japan All-Star Series. In November 2018, Ramírez elected to become a
free agent after clearing
waivers and being outrighted off the Mariners' 40-man roster.
Boston Red Sox On December 18, 2018, Ramírez signed a minor league contract with the
Boston Red Sox. He started the 2019 season with the
Triple-A Pawtucket Red Sox. On April 16, his contract was selected by Boston, and he made his Red Sox debut the same day, allowing four runs in three innings of relief during an 8–0 loss to the Yankees in New York. He was
designated for assignment on April 19, and sent outright back to Pawtucket on April 21. With Pawtucket during the 2019 season, Ramírez was 6–8 with a 4.74 ERA and 95 strikeouts in innings. He elected free agency on October 1.
New York Mets On January 26, 2020, Ramírez signed a minor league deal with the
New York Mets. He was called up to the Mets on September 4, 2020. Ramírez pitched in 6 games in 2020, notching a 0.63 ERA and 9 strikeouts over 14.1 innings pitched. Ramírez became a free agent on October 28, 2020.
Detroit Tigers On January 19, 2021, Ramírez signed a minor league contract with the
Detroit Tigers, with an invitation to spring training. On May 7, 2021, Ramírez was selected to the active roster. Ramírez appeared in 17 games for the Tigers, recording a 1-1 record with a 5.74 ERA with 20 strikeouts. On August 27, 2021, Ramírez was designated for assignment by the Tigers. On August 28, he was released by the Tigers.
Washington Nationals On March 13, 2022, Ramírez signed a minor league contract with the
Washington Nationals. Ramírez had a 4-2 record and a 2.92 ERA for the Nationals in 2022, starting two games and appearing in relief in 58 games. On December 21, 2022, Ramírez signed a contract worth $1 million for the 2023 season with up to $1 million available in performance bonuses. In 23 appearances for Washington, Ramírez struggled to a 6.33 ERA with only 13 strikeouts in 27.0 innings pitched. On June 7, 2023, Ramírez was designated for assignment by Washington after
Cory Abbott was recalled from Triple–A. He cleared waivers and was released on June 9.
Tampa Bay Rays (second stint) On June 12, 2023, Ramírez signed a minor league contract with the
Tampa Bay Rays organization and was assigned to the Triple–A
Durham Bulls. His contract was selected to the 40man roster on July 30. In 15 games for Tampa Bay, he struggled to a 6.48 ERA with 30 strikeouts in innings pitched. On September 30, Ramírez was
designated for assignment by Tampa Bay. He cleared waivers and was sent outright to Triple–A Durham on October 2. On October 13, Ramírez elected free agency. Ramírez re-signed with the Rays on a minor league contract on December 6, and began the 2024 season with Triple–A Durham. Ramírez was selected to the major league roster on April 20, 2024. In 11 games for the Rays, he compiled a 4.50 ERA with 9 strikeouts across 16 innings. On May 22, Ramírez was designated for assignment by Tampa Bay, and was sent outright to Durham on May 24 after clearing waivers. On August 26, the Rays called Ramírez back up to the major leagues. He was designated for assignment again on August 31. Ramírez cleared waivers and was sent outright to Durham on September 3. He elected free agency on October 4.
Minnesota Twins On February 15, 2025, Ramírez signed a minor league contract with the
Minnesota Twins. On March 8, it was announced that Ramírez would "miss significant time" due to tears in his
teres minor muscle and
lat muscle. Upon returning, he made 10 appearances split between the rookie-level
Florida Complex League Twins and Triple-A
St. Paul Saints. On August 1, the Twins selected Ramírez's contract, adding him to their active roster. In nine appearances for Minnesota, he recorded a 2.45 ERA with five strikeouts and one save over 11 innings of work. Ramírez was designated for assignment by the Twins on August 24. He cleared waivers and was sent outright to Triple-A St. Paul on August 26. On October 10, Ramírez elected free agency.
Algodoneros de Unión Laguna On April 3, 2026, Ramírez signed with the
Algodoneros de Unión Laguna of the
Mexican League. In one start for the Algodoneros, Ramírez threw five innings and gave up one earned run while striking out two batters.
Colorado Rockies On May 3, 2026, Ramirez's contract was purchased by the
Colorado Rockies organization. ==International career==