Amarista was signed by the Los Angeles Angels of Anaheim as an amateur free agent in 2007. He played in the Dominican Summer League in 2007 before playing with the Angels' rookie league and Class-A clubs in 2008. Amarista transitioned all the way from high-A to the Triple-A level in 2010. After starting 2011 with the Triple-A Salt Lake Bees, Amarista was called up to the majors for the first time on April 25, 2011. He made his first appearance on April 26, 2011 against the Oakland Athletics. In his first major league at bat, he doubled to drive in two runs. Amarista played in a total of 23 games with the Angels in 2011. Amarista opened 2012 as a utility infielder on the Angels 25-man roster but only played in a single game as a pinch runner before being optioned to AAA Salt Lake on April 13.
San Diego Padres
On May 3, 2012, Amarista and minor league pitcher Donn Roach were traded to the San Diego Padres for reliever Ernesto Frieri. After 11 games with the Triple-A Tucson Padres, Amarista was called up to the Padres on May 17 to play second base. Amarista was eventually supplanted by Logan Forsythe as the regular second baseman, but he continued to show his versatility by making occasional starts at second, shortstop, left field, and also in center field when Cameron Maybin was nursing a wrist injury. On June 28, 2012, Amarista hit his first career home-run, a grand slam off of Brett Myers, to cap off a six-run ninth inning in a victory against the Houston Astros. This began a brief power surge where Amarista hit 4 home runs and collected 11 RBI in five games. Amarista finished 2012 batting.240, with a.282 on-base percentage and five home runs in 275 at-bats. Amarista served a utility role for the Padres in 2013. He took most of the starts at second base while Chase Headley was injured to begin the year, and he made 53 starts in center field with Cameron Maybin absent for the majority of the season. He finished the year starting at shortstop when Ronny Cedeño sat out and ended 2013 with 84 starts and 146 games played. Amarista batted.236 with a.282 on-base percentage and five home runs in 368 at-bats. Amarista spent much of his time in the infield in 2014. He began the year making spot starts in center and around the infield and serving as a pinch hitter. On April 6, Amarista's birthday, he hit a 3-run pinch hit home run to defeat the Miami Marlins. Amarista picked up a handful of starts at third and second when Chase Headley was out with a strained calf in late April and early May. He saw more time at second and third in June when Jedd Gyorko was out with plantar fasciitis and Chase Headley sat with a herniated disc. When Everth Cabrera sat out with a hamstring injury on July 1, later spending significant time on the disabled list, Amarista began seeing regular time at shortstop. Amarista made 68 starts at the position from July 1 through the end of the year. He finished the season with a.239/.286/.314 batting line and five home runs, setting career highs in at-bats, games started, and games played. Amarista began 2015 as the Padres everyday shortstop, splitting time with Clint Barmes. He also made a handful of starts at second base and left field later in the year. On June 17th, Amarista pitched to one batter in the 8th inning of a blowout against the Oakland Athletics, retiring the only batter he faced on a flyout to right-field. For the year, he made 79 starts at short and played in 118 games overall, batting.204/.257/.287 with three home runs. Amarista started the 2016 season with Triple-A El Paso, but was called up within the first week of the season when Yangervis Solarte went to the disabled list. Amarista himself landed on the 15-day disabled list with a right hamstring strain on April 20. On May 31st, Amarista was once again brought in to pitch with 2 outs in the 8th inning of a blowout, this time against the Seattle Mariners, and retired the only batter he faced on a ground-out to second base. Amarista continued in a part-time role during June and was optioned to Triple-A on July 3. He bounced between Triple-A and the Majors in July, and then went to the disabled list after re-injuring his hamstring on August 1. Amarista returned in September in a utility role, playing the infield and outfield. He finished the season with a.257/.295/.271 batting line in 140 at-bats. He had 31 starts in the field, including at second base, shortstop, third, and left and right field.
Colorado Rockies
On January 17, 2017, Amarista signed a one-year, $1.1 million contract with the Colorado Rockies. On April 3, 2017, Amarista hit a RBI double in the eighth inning, pinch hitting for Adam Ottavino against the Milwaukee Brewers on Opening Day.
On January 24, 2018, the Detroit Tigers signed Amarista to a minor league contract with a non-roster invitation to spring training. He was released on March 24, and signed a minor league contract with the Philadelphia Phillies on March 26. He was released on July 3, 2018.
On March 19, 2019, Amarista signed with the New Britain Bees of the Atlantic League of Professional Baseball.
Sugar Land Skeeters
On November 6, 2019, Amarista was selected by the Sugar Land Skeeters in the New Britain Bees dispersal draft.
Personal life
Amarista was given the nickname "Little Ninja" by Padres catcher John Baker because, according to Baker, "Teams don't see Amarista coming. He sneaks up on them." Amarista's height is listed variously as 5'7" or 5'8".
