First capped as a teenager against France in 1949, his first moment of glory with Wales came in the Triple Crown clash with Ireland in Belfast on 11 March, 1950. The scores were tired at 3-3 with the Ravenhill clock showing a mere three minutes left to play.
Wales had beaten England at Twickenham and Scotland at St Helen's and were seeking a first Triple Crown since 1911. Thomas was on the left wing, waiting for his chance.
Former Western Mail rugby correspondent John Billott takes up the story: "Ireland heeled in their own 25. Jackie Kyle was bound to clear to touch. But Ray Cale pounced round the scrum to harass Carroll. As the scrum half desperately shovelled the ball out ot Kyle, Cale went with it. The ball rolled loose. Cleaver picked up and fed Lewis Jones: the winning try was taking shape.
"Lewis Jones, in his new position of centre, drew full back Norton and sent a long pass swinging out to Malcolm Thomas. There were 15 yards to go as the Welsh wing threw back his head and ran for the Triple Crown.
"Corner-flaggers streamed across like a cloud of locusts. They hit Thomas as he dived for the corner. Down everyone crashed, corner flag and all. Was it a try? There were agonising, hour-long seconds before referee RA Beattie (Scotland) raised his arm and Wales had won.
"If Irish touch-judge Ossie Glasgow had signalled that Thomas had knocked down the flag before grounding the ball there would have been few Welsh protests. It was a marginal decision either way."
Wales went on to complete their first Grand Slam since 1911 with a home win over France and Thomas also played in all four matches in the 1952 Grand Slam campaign.
One of the most versatile players of his era, he played centre, wing and outside half for Wales in 27 internationals between1949-59. He also played at wing, centre, outside half and full back for the British & Irish Lions on two tours Down Under in 1950 and 1959.
He captained Wales twice in 1957 and ended with two Grand Slams, two Triple Crowns and three outright Five Nations title wins in his outstanding career. He also scored 152 points in 32 matches for the Lions, playing in four Tests.