The 45-year-old singer tied the knot with Barry Herridge, 38, on her birthday at Las Vegas' Little White Wedding Chapel Thursday. The venue is the same spot where Britney Spears and Jason Alexander tied the knot in 2004.
It's the fourth marriage for the "Nothing Compares 2 U" singer, whose ex-husbands include music producer John Reynolds, journalist Nicholas Sommerlad and musician Steve Cooney.
O'Connor wore a pale pink dress for the drive-thru ceremony; Herridge wore a matching button-up shirt. An eyewitness tells Us Weekly the bride chose the locale because she "wanted a rock n' roll style wedding."
After the couple exchanged vows, "the staff at the chapel sang her 'Happy Birthday' and she started to tear-up a little," the eyewitness adds. "They were on their own and did not have any family or friends."
In her official blog, the singer -- who once claimed to be a lesbian -- said the wedding was "too glorious for words."
The Irish singer promised to give fans a full update on Sunday, because "for now. . .it's a bit of a 'Can't. Talk. C-ck. In. Mouth.' situation."