WWE star Jack Swagger was arrested last night in Mississippi, TMZ has learned -- after allegedly driving under the influence ... with pot in his car.

Sources close to the situation tell TMZ, Swagger -- real name Jacob Hager -- was leaving a "Smackdown" taping at Mississippi Coast Coliseum in Biloxi when he was pulled over for speeding.

According to law enforcement, the officer who pulled him over determined Swagger was driving under the influence -- and a search revealed Swagger was in possession of marijuana.

We're told Swagger -- a former WWE World Heavyweight champ -- was taken in by local police officers ... and later released on his own recognizance.

He has been charged with DUI (not alcohol), marijuana possession, and speeding -- all misdemeanors.

We reached out to WWE, who tells TMZ, "Mr. Swagger is responsible for his own personal actions."