The picture is the first glimpse of the titular couple's big day, which takes place in the CBS sitcom's season finale on May 14.
Speaking to TV Guide, executive producer Mark Roberts described the crystal and pearl satin gown as "really purty and elegant".
However, he also teased that Mike (Billy Gardell) and Molly will be confronted with "some unexpected twists and turns before they get to the altar".
Francis Guinan was recently cast as Mike's estranged father, who turns up at a rehearsal dinner in the penultimate episode of the season.
Mike & Molly was renewed by CBS along with 17 other shows last month.
The show currently airs Mondays at 9.30/8.30c.