Callista Gingrich has been the president and CEO of Gingrich Productions, a multimedia production and consulting company in Arlington, Virginia, since 2007.
She previously worked as a congressional aide in the House of Representatives and is president of The Gingrich Foundation, a charity organisation.
She is Newt Gingrich's third wife and he converted to Catholicism to marry her.
Ambassadors require Senate confirmation before assuming the role.
The announcement comes days before Trump arrives at the Vatican to meet Pope Francis.