Gavin Christopher Newsom was born in San Francisco, California, to Tessa Thomas (née Menzies) and William Alfred Newsom III, a retired state appeals court justice and attorney for Getty Oil. He is of mostly Irish descent; one of his maternal great-grandfathers, Scotsman Thomas Addis, was a pioneer scientist in the field of nephrology and a professor of medicine at Stanford University.

Newsom is the second cousin, twice removed, of musician Joanna Newsom.

After graduation, he co-founded businesses with family friend Gordon Getty, who was an investor.

Newsom began his political career in 1996 when San Francisco Mayor Willie Brown appointed him to serve on the city's Parking and Traffic Commission and as a member of the Board of Supervisors the following year.

he attended kindergarten and first grade at the French American bilingual school in San Francisco.

He eventually transferred because of severe dyslexia that still affects him.

At the time, he became the youngest member of San Francisco's board of supervisors and also, like Shelley before him, the board's only heterosexual Caucasian male.

Newsom was subsequently elected to a full four-year term to the board in 1998.

Newsom sold his share of his San Francisco businesses when he became mayor in 2004.

He maintained his ownership in the Plump Jack companies outside San Francisco that included the Plump Jack Winery in Oakville, California, new Plump Jack-owned Cade Winery in Angwin, California, and the Plump Jack Squaw Valley Inn.

As supervisor, Newsom had as his centerpiece a voter initiative called Care Not Cash (Measure N), which offered care, supportive housing, drug treatment, and help from behavioral health specialists for the homeless in lieu of direct cash aid from the state's general assistance program.