U.S. Supreme Court Justice Stephen Breyer officiated at the private 5 p.m. ceremony, held outdoors under a sunny sky.
Kennedy, son of the late Massachusetts Sen. Edward Kennedy, is a former eight-term Democratic congressman from Rhode Island. Petitgout, of Brigantine, N.J., teaches middle school.
"This is a day that's a beautiful day, not only in weather but just for my family," Kennedy, 44, told reporters before the wedding, according to the Cape Cod Times. "And I'm the luckiest guy. She's the best I could have ever imagined and I'm lucky to be able to share this day with her."
Kennedy wore a blue coat and white pants; his bride wore a white dress. About 200 friends and family were in attendance. Kennedy's brother, Edward Kennedy Jr., served as best man.
Since leaving Congress in January, Patrick Kennedy he has been named a visiting fellow at Brown University and has campaigned to improve brain research. He lives with Petitgout and her young daughter from a previous marriage.
Earlier in the day Friday, Kennedy and his brother spoke to reporters gathered outside the compound as they walked to a nearby dock.
"I'm taking the groom out for a little sail this afternoon to get him all relaxed and ready for the ceremony later," Edward Kennedy Jr. said, according to The Cape Cod Times.
Patrick Kennedy said he felt his father's presence before the wedding. Edward Kennedy Sr. died in 2009.
"I feel like my dad's kind of orchestrating everything from up above and he's doing a great job so far and he's telling us to get out on his sailboat and enjoy the ocean like he always did," he said.
