Both of Marc Mezvinsky's parents served in Congress.
This question just in from Jonathan Levy of Chicago:
With the announcement of Chelsea Clinton's engagement to Marc Mezvinsky, I wonder if this will be the first marriage where all four parents are current/former federal elected officials.
Indeed it will. Marc's father, Ed Mezvinsky, ousted Rep. Fred Schwengel (R-Iowa) in 1972 and wound up serving on the House Judiciary Committee during the impeachment hearings of President Nixon. In 1974, a big Democratic year nationally, he won re-election over Republican Jim Leach, but Leach turned the tables on him two years later. While still a member of Congress, he married Marjorie Margolies, a TV news reporter from Philadelphia. They moved to Montgomery County, Pa., after his defeat, and in 1980 he sought the Democratic nomination for the Senate, but he finished a weak fifth in the primary.
In 1992, in the wake of the Clarence Thomas-Anita Hill hearings, and following the retirement of Rep. Laurence Coughlin (R), it was Marjorie Margolies-Mezvinsky's turn for politics. She ran in the historically Republican district and narrowly defeated state Rep. Jon Fox. As fate would have it, she was the deciding vote in favor of President Clinton's 1993 budget package, which called for higher taxes. That vote helped seal her fate; two years later Fox came back and defeated her in another close race.
As for Chelsea Clinton's parents, I believe her father was elected president and her mother served in the Senate.