Mattson joined Ponsonby RFC in 1916, and was a member of their club side that won three consecutive junior Auckland championship titles, in 1919, 1920 and 1921.[4] He made his provincial debut for Auckland in 1922, playing in four matches, but he missed the following two seasons due to injury; a knee injury in 1923 and a broken jaw the next year.[1]
In 1925, with none of the members of "The Invincibles" that toured the British Isles and France in 1924–1925 considered for selection, Mattson was picked for the All Blacks team to tour New South Wales after showing good form at club level. He played six matches for the All Blacks on that tour, although troubled by a knee injury, including all three of the games against New South Wales,[1][4] where Sydney papers described him as "brilliant".[5][6] He scored his only points for the All Blacks, a try, in the tourists' first match, against Wellington at Athletic Park before their departure for Australia.[4][7][8]
After the tour to New South Wales, Mattson played a further five games for Auckland. In a match against Canterbury, he scored four tries, which as of 2024 remains the most tries scored by an Auckland player against Canterbury. The feat has been equalled by Bernie Fraser and Joeli Vidiri, but not surpassed.[4] In total, Mattson scored eight tries in his nine appearances for Auckland.[9]
After playing "several brilliant games on the wing" for Ponsonby in 1925, Mattson temporarily retired from rugby in 1926 because of his old knee injury.[10] After two seasons off, Mattson returned to Ponsonby, but he broke his collarbone in his first reappearance on 28 April 1928 at a match at Eden Park.[11] He retained an interest in rugby, serving as treasurer of the Ponsonby club and inaugural president of the Ponsonby Old Boys' Association.[4] He also coached the Parnell club.[1]
