Mattheou was born in Thessaloniki on July 12, 1924. He debuted for Aris in 1946 and transferred to Panathinaikos in 1950. On March 30, 1955, he quit Panathinaikos and joined Panionios. Later, he went to Italy for post-graduate studies. While there, he played for Varese. On his return to Athens in 1957, he signed for Sporting as a player-coach. He quit in 1960.
He was capped 44 times in his career scoring 529 points.
Mattheou coached the National Basketball Team of Greece between 1958 and 1973. His over all record with all teams (Men, Women, Under-21) was 56 victories against 56 defeats. On the club level, besides Sporting, he coached Olympiakos and PAOK.
In 2002, Mattheou authored a personal autobiography entitled "60 Years in Greek Basketball".