The announcement, made to fans Monday on Hayes' web site, offered a rare insight into his private life, which he has long kept under wraps.
"As so many of you have given me your heart and soul over the past 10 years I thought it only fitting that I too return the respect and inform you of the most significant event in my life," Hayes wrote.
"On June 19th 2006 I married my boyfriend of two years, Richard (Cullen), in a civil partnership ceremony in London. I can honestly say it was the happiest day of my life."
While Hayes said he finally felt "secure and content" in his heart, he reaffirmed his belief that "families and relationships are not commodities to be sold off for public consumption," and would therefore remain "a public person with a private life." He was briefly married in the late 1990s to a longtime female friend.
On the professional side, the 34-year-old is about to spend six months in London recording his third solo album for an unspecified new label. He announced earlier this month that he had split with his home of 10 years, Columbia Records.
Singer/songwriter Hayes and producer/multi-instrumentalist Daniel Jones formed Savage Garden in 1994. Their two albums, 1997's self-titled debut and 1999's "Affirmation" sold more than 23 million copies combined worldwide.
The duo also topped the U.S. singles charts with the tunes "I Knew I Loved You" and "Truly, Madly, Deeply." They split in 2001, and Hayes released his solo debut, "Spin," the following year.