Sen. Tom Duane, who made history in 1998 as the first openly gay individual elected to the state Senate and the first HIV-positive person elected to office in the nation, has decided not to seek re-election.

According to a press advisory released by his office, Duane, a Democrat who represents the 29th SD in Manhattan, will formally announce his decision at noon tomorrow outside the NYC HIV/AIDS Services Administration offices. (400 Eighth Ave., between 29th and 30th).

Duane’s announcement comes just before petitioning is scheduled to start (on June 5). It’s rather abrupt and caught insiders – including the senator’s Democratic colleagues – by surprise.

A source familiar with Duane’s decision says the senator simply decided that 14 years in Albany was quite enough, thank you, and he’s had quite enough of the weekly trip upstate.

His departure will certainly be a blow to the conference. He was not only an outspoken advocate for gay rights, having carried the same-sex marriage bill for years, but also a number of other liberal causes – including a bill to legalize medical marijuana.

Come to think of it, Duane’s decision to quit the Senate may have been foreshadowed when he turned the med-mar bill over to Sen. Diane Savino, a Staten Island Democrat and one of four IDC members.

Duane was certainly an outsized presence in Albany. His 2009 post-3 a.m. floor speech in which he delivered an impassion plea for passage of a bill that would cap rent and utilities for low-income people living with AIDS will not soon be forgotten. (The bill passed).

This is a safe Democratic seat, but there’s likely to be a battle for it.

A number of NYC electeds live in Duane’s district, including NYC Council Speaker Christine Quinn, who once worked for Duane when he was a councilman. But she’s the frontrunner in the 2013 NYC mayor’s race right now, and is not likely to give that up.

NYC Councilwoman Gale Brewer lives in the district, as does NYC Councilman Dan Garodnick, who is laying the groundwork for a 2013 run for NYC comptroller.

Four candidates have emerged for Quinn’s Council seat: Yetta Kurland, Brad Hoylman, Andrew Berman and Corey Johnson. All of them are identified with the LGBT community.

It’s possible one of them – or perhaps someone else entirely – will decide to shift focus and run for Duane’s seat.

The seat is not necessary reserved for a gay candidate. It was previously held by Catherine Abate, who is married to a man (or at least, she was). Abate gave up her seat for an unsuccessful run for state attorney general.

The race was eventually won by Eliot Spitzer, who defeated the GOP incumbent, Dennis Vacco, in a squaker.

UPDATE, or rather, clarifications: Two are needed.

1) Duane revealed he was HIV positive during his successful 1991 campaign for the NYC Council – long before he ran for the Senate.

2) Brewer does not live in the newly-drawn version of Duane’s district. As noted by a commenter, she could run this year from her current location, but would eventually have to move into the district.

Also in Duane’s district and potential candidates for his Senate seat: Assembly members Deborah Glick and Brian Kavanaugh.