Álvarez signed with the Philadelphia Phillies as an amateur free agent on January 8, 2007. From 2007-2009 he played entirely with the Dominican Summer League Phillies. In 2007, Álvarez finished with a 1-3 record, 4.46 ERA in 11 games. In 2008, he finished with a 4-2 record, 3.23 ERA in 18 games. In 2009, he finished with a 3-4 record, 2.59 ERA in 14 games. On August 18, 2009, he was released by the Philadelphia Phillies.
On January 13, 2013, Álvarez was signed as a free agent with the New York Mets. Álvarez played in the minors with the Brooklyn Cyclones, Savannah Sand Gnats, St. Lucie Mets and the Binghamton Mets. Álvarez was called up to the majors for the first time on September 1. He made his major league debut on September 3 against the Miami Marlins. The Mets won the game 4-3 with Alvarez giving up an RBI single to Christian Yelich which the tied the game for the Marlins with him being charged with a blown save. Álvarez finished the season with a 13.50 ERA in 4 games in 1.1 innings pitched while giving up 4 hits, 2 runs, and one home run while only getting one strikeout with a WHIP of 3.000.
2015
Álvarez was promoted up to the majors on August 22 with first basemanLucas Duda going on the disable list with a back injury. On August 23 he was sent back to the Las Vegas 51s to make room for David Wright who was making his return from Spinal stenosis. He did not make a single appearance when he was called up a day earlier. He was recalled on September 4 to be available to pitch against the Miami Marlins. On September 7, Álvarez got his first career win against the Washington Nationals by striking out outfielder Bryce Harper in the bottom of the 6th inning. On September 15, Álvarez strained his groin with one out in the eight inning against the Marlins forcing him to leave in what would be a 3-9 loss for the Mets. He had allowed 3 hits and exited the game after stumbling and failing to deliver a pitch, which resulted in a balk. On September 18 it was revealed that Álvarez was headed to Port St. Lucie to rehab the groin injury he had sustained three days ago and that it was unlikely for him to pitch again in 2015. Álvarez finished the season with a 1-0 record, 12.27 ERA in 6 games in 3.2 innings pitched while giving up 5 hits, 5 runs, 2 home runs, 1 walk, and 1 balk while getting two strikeouts with a WHIP of 1.636. On May 23, 2016, he was designated for assignment.
Atlanta Braves
The Braves claimed Alvarez off waivers on May 25, 2016. He was optioned down to their AAA affiliate, the Gwinnett Braves and called up to Atlanta on June 14.
Texas Rangers
On July 27, 2016, the Braves traded Álvarez and Lucas Harrell to the Texas Rangers for Travis Demeritte. After two appearances with the Rangers, he was demoted to Triple-A Round Rock on August 4, 2016. He elected free agency on November 6, 2017.
