Luis Castillo or Luis Miguel Castillo (born December 12, 1992) is a Dominican professional baseball pitcher for the Seattle Mariners of Major League Baseball (MLB). Luis Castillo made his MLB debut in 2017 with the Cincinnati Reds. Castillo is a two-time All-Star.
Castillo signed with the San Francisco Giants as an international free agent in December 2011. Luis Castillo made his professional debut in 2012 with the DSL Giants and spent the whole season there, going 1–3 with a 3.31 ERA in 54.1 relief innings pitched. In 2013, Luis Castillo returned there, going 0–1 with a 0.64 ERA in 27 relief appearances, and in 2014, Luis Castillo played for the Augusta GreenJackets where Luis Castillo pitched to a 2–2 record and 3.07 ERA in 48 relief appearances.
On December 20, 2014, Castillo along with Kendry Flores were traded to the Miami Marlins for Casey McGehee. Luis Castillo spent 2015 with the Greensboro Grasshoppers and was promoted to the Jupiter Hammerheads in July. In 35 games (16 starts) between the two teams, Luis Castillo was 6–6 with a 3.20 ERA.

Castillo began 2016 with Jupiter and was promoted to the Jacksonville Suns during the season. On July 29, 2016, the Marlins traded Castillo along with Jarred Cosart, Josh Naylor and Carter Capps to the San Diego Padres for Andrew Cashner, Colin Rea and Tayron Guerrero. Luis Castillo was returned to Marlins after Rea suffered an injury in his first start and was returned to the Padres. The Marlins added him to their 40-man roster after the season. In 26 games (24 starts) between Jupiter and Jacksonville, Luis Castillo was 8–6 with a 2.26 ERA.