The Rhode Island Democrat taped a message to be aired on the state's television stations Sunday night. The Associated Press viewed the message Thursday, ahead of the announcement.
"Now having spent two decades in politics, my life is taking a new direction, and I will not be a candidate for re-election this year," Kennedy says in the ad.
The decision by the eight-term congressman comes less than a month after a stunning Republican upset in the race for the Massachusetts Senate seat his father held for almost half a century.
Patrick Kennedy has been in and out of treatment for substance abuse since crashing his car outside the U.S Capitol in 2006. Still, he has been comfortably re-elected twice since then, after making mental health care his signature issue in Washington.
In the taped message, Kennedy says he remains committed to public service. He also thanked Rhode Island voters for supporting him through ups and downs.
"When I made missteps or suffered setbacks, you responded not with contempt, but compassion," he said. "Thank you for all the times you lifted me up, pushed me forward."
He was not specific about his plans, but said he would continue to fight for issues including on behalf of those suffering from depression, addiction autism and post-traumatic stress disorder.