Hines, 48, has been married once before, while this will mark wedding No. 3 for Kennedy Jr., 60.
The two have also been seen promoting each other's causes.
"It's fun to have a partner," she explained to Us in April. "He's so dedicated to the environment and clean water, so we take turns. He'll come to my United Cerebral Palsy event and walk the red carpet with me. It's a good match up."