The Diamondbacks invited Pollock to spring training in 2010. He broke his right elbow while attempting to make a diving catch. Pollock missed the entire season due to the injury.

Pollock was called up to the majors for the first time on April 18, 2012, and made his debut that day. Batting as a pinch hitter for Justin Upton, Pollock collected his first career MLB hit, a single, on April 23 against the Phillies. He played in 31 games that season for the Diamondbacks, batting .247 with two home runs and eight RBIs.

In 2013, Pollock batted .269 with eight home runs and 38 RBIs the course of 137 games.

Pollock became engaged to his girlfriend, Kate, in March 2014. They met at Notre Dame, where Kate played for the lacrosse team. They were married after the 2014 season. In May of 2020, Pollock and his wife welcomed a baby girl at only 24 weeks old.

In 2015, he was named a National League All-Star. He ended the season batting .315 with 20 home runs and 76 RBIs. He led the National League in power-speed number (26.4). Pollock signed to a two-year contract extension worth $10.25 million on February 8, 2016. Pollock broke his right elbow again at the end of spring training, this time on a slide at home plate, and missed most of the 2016 season. In the 12 games he would appear in during the 2016 season, Pollock would record 10 hits on 41 at bats, a .244 batting average.

On May 15, 2017, Pollock was placed on the 10-day disabled list due to a right groin strain. Over the course of 112 games in 2017, Pollock would record a batting average of .266, 14 home runs, and 49 RBI.

In 2018, Pollock hit .257 with 21 home runs and 65 RBIs over 113 games. He was also 13 for 15 in stolen base opportunities.

On January 26, 2019, the Los Angeles Dodgers announced that they had signed Pollock to a four-year contract, with a player option for another year.

On April 30, 2019, the Dodgers placed Pollock on the injured list with a right elbow inflammation. He did not rejoin the team until July 12. In September, the Dodgers moved Pollock to left field for the rest of the season. For the season he appeared in 86 games, batting .266/.327/.468, with 15 homers and 47 RBIs.

The 2020 season was shortened because of the COVID-19 pandemic, but Pollock played in 55 of the Dodgers’ 60 games. On September 16, Pollock hit his 100th career home run, off of Adrián Morejón of the San Diego Padres. He batted .276/.314 (a career low)/.566 (a career high) with 16 home runs and 34 RBIs. In the postseason, Pollock had one hit (a double) in five at-bats in the Wild Card Series, three hits in 10 at-bats in the 2020 NLDS, four hits in 20 at-bats in the 2020 NLCS and one hit (a double) in six at-bats in the 2020 World Series, which the Dodgers won in six games.