[3] From 2004 to 2005, Ramírez served as a law clerk for Judge Warren J. Ferguson of the United States Court of Appeals for the Ninth Circuit.

In 2009, Ramírez joined the United States Department of Justice, serving as counsel to then-Assistant Secretary Tom Perez.

[5] In 2021, Ramírez became president of the nonprofit Public Counsel, a pro bono law firm, and left in 2023 to become a federal judge.

[7][8] In 2018, Ramírez represented the California state legislature as amicus curiae in a Chicago suit challenging Attorney General Jeff Sessions' conditioning of grants to the end of sanctuary city policies.

Although charged with no crime, the Orange County Sheriff's Office turned him over to U.S. Immigration and Customs Enforcement, and he was held for nine months in ICE's Adelanto Detention Center.