A front-row forward and lock, he played provincial rugby for both Wellington and Marlborough, and was involved in services matches during World War II.

[5] He won two New Zealand Rowing Championships titles representing Wairau: the single scull in 1949 at Lake Karapiro,[9] and as a member of the men's coxed four crew in 1954 in Picton.

[10] At the 1950 British Empire Games in Auckland, Hegglun, as reigning national champion, represented New Zealand in the single scull, finishing in fourth place.

[17] When Marlborough successfully defended the shield against Golden Bay-Motueka the following month, by 24 points to 3, Hegglun's forward play was described as "outstanding".

[2][28] While serving in the Middle East, Hegglun took part in services rugby matches, representing 2NZEF, including against a British Combined Services team and an Australian Imperial Force side in December 1941,[29][30] He also played a prominent part in the inaugural rowing regatta in 1942 between New Zealand forces and the Cairo River Club for the Freyberg Cup, held on the Nile.

[32] Hegglun also showed some talent as a boxer, contesting the heavyweight class in the New Zealand divisional boxing championships in Syria in 1942, where he was knocked out in the semi-final.

[33] Following the war, Hegglun remained active in the military, serving in the Royal New Zealand Infantry Regiment Territorial Force, rising to the rank of colonel.