The San Diego Padres selected him in the fourth round of the 2012 Major League Baseball draft, and the parties agreed on a $340,000 signing bonus. He spent 2012 with the Arizona League Padres, pitching to a 4.34 earned run average in innings. He pitched only innings in 2013 and innings in 2014 due to injuries. Lockett returned in 2015 and pitched for the Fort Wayne TinCaps, Tri-City Dust Devils, and AZL Padres, posting a combined 4-4 record and 4.14 ERA in 18 total games between the three clubs. In 2016, he played for Fort Wayne, the Lake Elsinore Storm, San Antonio Missions and El Paso Chihuahuas, compiling a combined 10-9 record, 2.96 ERA and 1.06 WHIP in 28 total games. The Padres added Lockett to their 40-man roster after the 2016 season. He spent 2017 with El Paso, collecting a 5-2 record and 4.39 ERA in ten starts. He missed nearly three months of the season due to a lower back strain. On June 1, 2018, Lockett was recalled by the Padres to start that evening in place of an injured Joey Lucchesi against the Cincinnati Reds. Through the first three innings, Lockett held the Reds to just one run on one hit and three walks. A lead off walk to Eugenio Suarez in the fourth, followed by a single by Scott Schebler and a double by Jose Peraza increased the Reds' lead to 3-0. Lockett came back to retire the next two batters before issuing his fifth walk of the day to Jesse Winker. Tucker Barnhart followed with a single to score Peraza, and knock Lockett out of the game. All told, Lockett allowed four hits, four runs and walked five in innings, taking the loss as the Reds defeated the Padres 7-2. For the season, Lockett went 0-3 with a 9.60 ERA in four appearances.
New York Mets
The Padres traded Lockett to the Cleveland Indians on November 20, 2018 for minor league pitcher Ignacio Feliz. On January 6, 2019, Cleveland traded Lockett and Sam Haggerty to the New York Mets for catcherKevin Plawecki. After beginning the season with the triple ASyracuse Mets, Lockett was called up in late June when Noah Syndergaard was placed on the 10 day injured list with a right hamstring strain. After cruising through his first two innings of work, Lockett was roughed up by the Chicago Cubs in the third. The Cubs scored six runs, all earned, to pin a loss on Lockett in his Mets debut. He earned his first career win a month later against Jeff Samardzija and the San Francisco Giants. Lockett pitched five innings, allowing one earned run with three strikeouts. Coincidentally, the one run was driven in by Joe Panik, who would become his teammate with the Mets later in the season.
