José Antonio Romualdo Pacheco was a Californio, born in Santa Barbara, California, to a family with prominent connections.

After the death of his father, Romualdo's mother married Captain John D. Wilson, a Scotsman, who sent Pacheco to Honolulu, Hawaii, for his education.

The Mexican–American War broke out two years later, and he was briefly held by American forces during the Conquest of California while on one trip in July 1846, as he brought cargo to Yerba Buena (modern day San Francisco).

Pacheco's association with a prominent family in the state helped him to gain support as he entered politics in the 1850s.

During the American Civil War Pacheco was appointed the rank of brigadier general by Governor Leland Stanford and directed to disarm military companies in the Los Angeles area that were not loyal to the Union.

After his brief tenure as governor, Pacheco ran for a U.S. House seat in 1876, defeating incumbent Peter D. Wigginton by just one vote.

After leaving Congress, Pacheco lived on a cattle ranch in the northern Mexican state of Coahuila for five years until he was appointed as U.S. Minister to various countries in Central America in 1890.