The announcement is expected to come at an 12:30 p.m. press conference tomorrow that The Donald is holding.
The move is a bit unexpected since Trump had talked even within the past few days about how he may be compelled to run a third-party campaign of his own if he didn't see a Republican candidate who he thought could beat President Barack Obama.
Gingrich is the longer-shot choice in a field in which Mitt Romney has re-established himself as the frontrunner after a commanding win in Florida.
Trump was courted repeatedly by several of the GOP hopefuls. Gingrich, when he was soaring in his first rise before the Iowa caucuses, made a trek to Trump's Fifth Avenue office in Manhattan to ask for his support.
Instead of an endorsement, they emerged with Gingrich saying he'd gotten Trump to agree to an "Apprenticeship" (get it?) program in poorer New York City schools.
The endorsement gives Gingrich a needed dose of free media from the person who became the first to channel, in the GOP field, the desire by the grass roots to find a nominee who could take the fight to Obama.