The longtime conservative political pundit -- who's worked on both FOX and CNN -- passed away Thursday ... this according to his wife, Debi. The exact details of his passing weren't immediately revealed ... but the news was first broken by none other than Donald Trump.

The 45th President of the United States made the announcement on Truth Social first ... calling LD a friend and incredible journalist who really understood the world.

Trump extended condolences to Lou's wife and their kids ... finishing off by saying Dobbs would be greatly missed.

A rep for FOX News Media, meanwhile, says ... "We are deeply saddened by the passing of Lou Dobbs. An incredible business mind with a gift for broadcasting, Lou helped pioneer cable news into a successful and influential industry. We are immensely grateful for his many contributions and send our heartfelt condolences to his family."

Dobbs rose to prominence after making the jump from local to national news in 1980 ... becoming one of the earliest journalists to sign on at then newly-formed cable news channel CNN.

He became the chief economics correspondent and a major force at the network for the next two decades before a disagreement on how to cover the infamous Columbine shooting led to a hasty exit from the network.

He returned to CNN just two years later in 2001 and spent another eight years at CNN before leaving for good.

Dobbs regularly spoke his mind on-air, promoting numerous controversial views and theories over the years. Most notably, devoting significant swaths of time to conspiracy theories about where President Barack Obama was born.

Dobbs voiced full-throated support for DT early on during his first presidency and continued to until he died, posting multiple times in recent days about Trump's resiliency -- and conspiracy theories surrounding the shooting in Butler, PA.

Dobbs was 78.