Get set for a gay old time at Brooklyn Borough Hall.

Borough President Marty Markowitz is offering up Borough Hall’s grand rotunda Sunday to host the city’s largest-ever gay wedding expo –and the Big Apple’s first-ever to be organized by government leaders.

The expo will feature 75 vendors – including designers, photographers stylists and bakeries — catering to lesbian, gay, transgender and bisexual couples.

“Get ready for over-the-top hairstyles, headdresses and wedding gowns from the 30s, 40s and 60s,” said Alice Sena, owner of Sposabella Couture bridal shop in Park Slope, which is running the expo’s fashion show.

She said the show would include females in tuxedos — a feature that’s been prominently displayed in her storefront since gay weddings became legal last year — and hopes to find male models willing to dress in wedding gowns also.

“I’ve been really trying but I still need two if anyone is interested,” she told the Post.

The expo runs from 10 am to 6 pm.