His signing bonus of just $17,000 was relatively tiny compared to most other contemporaneous Latin American prospects that would reach his same level of success in the minor leagues.

[4][5] He appeared in the 2016 All-Star Futures Game, retiring all three batters he faced as a pitcher for Team World.

[6] On July 17, 2016, Nationals manager Dusty Baker announced López would be called up to make his major league debut with a start on July 19, 2016, against the Los Angeles Dodgers at Nationals Park in Washington, D.C.[7] During the game, he gave up a lead-off home run to Chase Utley, allowed three runs in the first inning, and gave up hits to seven of the first 11 batters he faced.

On December 7, 2016, López was traded with Lucas Giolito and Dane Dunning to the Chicago White Sox in exchange for Adam Eaton.

In 2019, he was 10–15 with a 5.38 ERA, and gave up the longest home run of the season in the major leagues, a 505-foot homer.

[17] With the 2020 Chicago White Sox, López appeared in eight games, compiling a 1–3 record with 6.49 ERA and 24 strikeouts in 26+1⁄3 innings pitched.

He was called up on July 16 where he made his season debut coming out of the bullpen going 2 innings, gave up 1 hit, and struck out 1.

[25][26] On March 18, 2024, López was given the fifth rotation spot for the major league roster after Bryce Elder and Huascar Ynoa were cut from the spring training camp.

[27] López was selected to his first All-Star Game roster as a reserve, alongside teammates Marcell Ozuna, Chris Sale and late add Max Fried.

[30][31] While at 6 feet tall, Lopez is not especially tall for a pitcher—some media stories highlighting Nationals pitching prospects before both pitchers' MLB debuts made note of the height disparity between Lopez and his Harrisburg teammate, 6-foot-6-inches Lucas Giolito[32][33]—he generates exceptional velocity on his fastball, which he can throw consistently above 95 mph and flash in the triple digits.

[39][40] After each completed inning he pitches, López points toward the sky, an action reflecting his Christian faith.