In 1946, his Father bought Central Cartage Company, which would later become Central Transport, and Moroun started working with him. During college, Matty regularly commuted between the University of Notre Dame in South Bend, Indiana, and Detroit to help run the family Business. He graduated in 1949 with a bachelor's degree in chemistry.
Moroun bought the Ambassador Bridge in 1979 when shares came on the market. It was originally privately built by railroad interests.
The bridge is now estimated to be worth between $1.5 and 3 billion. CenTra, Inc., is also the controlling body of Central Transport International, an LTL trucking carrier. Moroun also has a controlling stake in Universal Truckload Services Inc., which is a holding company for several over-the-road truck lines and Logistics companies (Universal Am-Can Ltd., Mason Dixon Lines, Economy Transport, Cavalry Logistics, Louisiana Transportation, Inc. etc.) Moroun is also the owner of the derelict Michigan Central Station for railroad Passenger traffic and the Roosevelt Warehouse. A 2008 Forbes article listed him as the 321st richest American.
The US and Canadian governments have agreed to build the Gordie Howe International Bridge, a bridge between Detroit and Windsor to be located downriver. On 25 March 2010, Moroun announced a suit to try to block construction of the new bridge, as it would compete with his own proposal to build a second span of the Ambassador Bridge, which he would own. Critics suggest that Moroun's opposition is fueled by the prospect of lost profits from duty-free gasoline sales at the bridge.
In 2009, the Michigan Department of Transportation (MDOT) sued Moroun and the Detroit International Bridge Company for failing to comply with the terms of a contract to construct ramps connecting the Ambassador Bridge to nearby expressways as part of the Gateway Project. Wayne County Circuit Judge Prentis Edwards ruled in February 2010 that Moroun and the chief deputy of the Detroit International Bridge Co., Dan Stamper, were in violation of the contract and ordered them to become in compliance. On 12 January 2012, Judge Edwards found both Moroun and Stamper to be in non-compliance with his previous order and ordered both men to jail, denying a motion to stay the order until it could be appealed to the Michigan Court of Appeals. After spending a night in jail, both men were released by the appellate court while they heard the case.