He and his twin brother Francisco de Haro were the eldest sons and first set of twins born to Don Francisco de Haro and Emiliana "Miliana" de los Reyes Sanchez.

Their maternal grandfather was Jose Antonio Sanchez who, along with his father (also named Jose Antonio Sanchez) arrived with the Anza Expedition of March, 1776. In his old age, their grandfather received a land grant for Rancho Buri Buri, 59 square kilometers (14,639 acres) in present day San Mateo county.

The twin brothers were born in Yerba Buena in Alta California, Mexico (later, San Francisco, California, United States).

Their mother gave birth to two sets of twins. Twins Ramon and Francisco were elder brothers to twins Carlotta and Candelaria, who were born in 1834. Their mother Miliana died in 1842, after the birth of her 12th child.

Ramon and his twin were murdered along with their "uncle" (an elderly cousin on their mother's side) José de los Reyes Berreyesa, shortly after landing in Marin county, having left San Francisco to accompany their uncle on his trip to visit family in Sonoma.

The twins held the land grant for Potrero de San Francisco, 9 square kilometers (2,229 acres) which included present day Potrero Hill, in San Francisco. Their murder and their family's subsequent loss of the land grant resulted in the U.S. Supreme Court opinion, De Haro v. United States, 72 U.S. 5 Wall. 599 (1866).

In addition, their murder was used against John C. Fremont, when he ran in 1856 as the Republican party candidate for U.S. president against James Buchanan. Fremont was responsible for their murder.

Fremont lost the presidential election in part because of this "military blunder" which was only one of many incidences in Fremont's career which displayed both poor judgment and a disregard for human life.