Principal photography on a biopic of San Francisco gay activist Harvey Milk will begin in January with Sean Penn in the lead role, it has been announced.

Milk, directed by Gus Van Sant, will begin shooting on location in the city ahead of a rival movie.

The Mayor of Castro Street, which has been in development for more than 15 years, is due to be helmed by X-Men director Bryan Singer.

Van Sant directed My Own Private Idaho, Drugstore Cowboy and Only Cowgirls Get The Blues.

Harvey Milk was probably the first out gay male politician in American history.

Known during his lifetime as “The Mayor of Castro Street,” he is regarded as a political icon amongst gay activists for his ability to build the LGBT community into a grassroots political force.

Milk was elected to the San Francisco Board of Supervisors in 1977.

In his 11 months in office he sponsored a gay rights bill and helped to defeat a proposition that would have seen openly gay and lesbian teachers sacked.

He was gunned down at City Hall by Dan White, a disgruntled former Supervisor, on November 27th 1978.

It had been reported that Matt Damon will play White in the Van Sant biopic but he has dropped out of the project due to scheduling conflicts.

White also killed the city’s mayor in his gun rampage.

Milk was recently honoured with a bust on permanent display in San Francisco City Hall, a rare accolade for someone who never held the position of Mayor.

It will be a permanent reminder of the unique place the city of San Francisco had in forming a new, politically active gay identity in the 1970s.

Milk had foreseen his own untimely death, and made several audio tapes to be played if he was assassinated.

One had recorded upon it his most famous statement, “If a bullet should enter my brain, let that bullet destroy every closet door.”

When White only received seven years in jail for Milk’s murder, San Francisco’s gay community rioted. More than 160 people were injured.

Many gay and lesbian community institutions are named in his honour, among them the Harvey Milk Plaza in San Francisco, the Harvey Milk Institute, the Harvey Milk Lesbian, Gay, Bisexual and Transgender Democratic Club, and the Harvey Milk High School in New York City.