See biographies by J. Lynch (1911) and D. A. Williams (1969).
He was born in Washington, D.C., the son of an Irish stonecutter who had immigrated to the United States in order to work on the United States Capitol. Broderick moved with his parents to New York City in 1823, where he attended public schools.
He was apprenticed to a stonecutter when young. In 1846 he ran for election to the United States House of Representatives, but did not win the election. He moved to California in 1849 and engaged in smelting and assaying gold. Broderick began the minting of gold coins, with less value of gold in them than their face value. His $10 coins, for example, only had $8 worth of gold in them. He used the profits to finance his political aspirations.
He was a member of the California State Senate from 1850–1851, serving as its president in 1851. Broderick was elected as a Democrat to the United States Senate and served there beginning March 4, 1857.
At that time, just prior to the start of the American Civil War, the Democratic Party of California was divided between pro-slavery and "Free Soil" advocates. Broderick represented the Free Soil faction. One of his closest friends was David S. Terry, formerly the Chief Justice of the California State Supreme Court, an advocate of the extension of slavery into California. Terry lost his re-election bid because of his slavery platform, and he blamed Broderick for the loss.
Terry made some inflammatory remarks at a party convention in Sacramento, which Broderick read. He took offense, and sent his former friend, Terry, an equally vitriolic reply. Passions escalated, and on September 13, 1859, Terry and Broderick met outside of the San Francisco city limits at Lake Merced for a duel.
The pistols chosen for the duel had hair triggers, and Broderick's discharged prior to the final "one - two - three" count, firing harmlessly into the ground. Thus disarmed, he was forced to stand as Terry shot him. Terry believed the shot to be only a flesh wound, but in fact, it proved mortal. Broderick died three days later. Some maintain that his death made him a martyr, and the episode represents another small contribution to the spiral towards Civil War.
He was buried under a monument erected by the state in Lone Mountain Cemetery, San Francisco. The town of Broderick, California and Broderick Street in San Francisco were named in his honor.