Frank, 71, and partner Jim Ready have not said when the wedding will take place, but confirm the ceremony will be held in Massachusetts, the Boston Herald reported.
"We don't have any more details at this time," said Frank's spokesman Harry Gural.
Frank, who has held his district's seat in Newton for 31 years, said last year he wouldn't seek a 17th congressional term, saying redistricting played a role in his decision. He said the stress of the job and a desire to spend more time with Ready were also contributing factors, The Washington Post reported.
"I have a partner now," Frank told Charlie Rose in a recent interview. "I'm in love for the first time in my life."
The relationship caught national attention in 2007 when Ready was charged with having marijuana plants in his home and again in 2010 when he taunted Frank's Republican challenger Sean Bielat at a public forum, the Post said.