[1] Kirwan was a telegraphist who worked in Tokomaru Bay on the East Coast of the North Island in 1914 when he was 18 years of age.

[2] Jack Kirwan moved to Tokomaru on the East Coast of the North Island in November 1914 where he began working at the local post office.

[10] Tragedy struck Kirwan and his family in early January 1919 when his sister Anastasia passed away after contracting influenza during the tail end of the 1918 pandemic.

[17] He was then selected in the combined Hawke's Bay-Poverty Bay team to play against the touring South African international side.

[22] He finished the representative season off with a defence of the Ranfurly Shield against Bay of Plenty at Nelson Park in Hastings which they won narrowly 17–16.

[24] In 1924 Kirwan played in a 6–0 loss to Wairarapa on 21 July, and then a 10–6 win over Wellington in their second shield defence of the season at McLean Park in Napier before a crowd of 6,000.

[27] The team Kirwan was in was a combined East Coast-Poverty Bay-Hawke's Bay side and they won comfortably by 32 points to 15.

[29] The match with Auckland was played in front of a huge crowd of 10,000 and Kirwan was heavily involved in several attacking raids.

Kirwan set up the Auckland Province side's first try with a reverse pass to Bert Cooke who scored under the posts.

[35] The rest of the first half of Kirwan's season was spent playing for his Marist side in the local club competition.

The match against Hawke's Bay was a Ranfurly Shield challenge with Kirwan kicking a drop goal on his old ‘home field’ of McLean Park, Napier.

Kirwan was reportedly unhappy with the lack of compensation provided for players in the representative team who often had to take time off work to play thus resulting in a loss in wages.

This is cited at one of the main reasons Kirwan then transferred to the rugby league code which was much more proactive in compensating its players for any loss in wages through playing the game.

[36] In mid to late September Kirwan switched codes and joined the Marist Old Boys rugby league team.

The move caused some controversy with a The New Zealand Herald article stating that "his inclusion was the source of a good deal of comment, and it is thought by many that, in the circumstances, the fact that he took part in a game with a direct bearing on the championship, was not according to the ethics of true sportsmanship.

"[37] Kirwan scored a try in a 20–17 win on Carlaw Park in front of an enormous crowd of 17,000 which was a club record for Auckland Rugby League at that time.

Devonport were also trying to secure rugby players to join their side including Tonkin, Matson (Ponsonby) and Neil Ifwerson (Grammar).

A loss to Devonport in the Roope Rooster competition and a 10–10 drawn match with City Rovers as part of the Labour Day celebrations.

The Marist season was over shadowed by the death of Bill Stormont who passed away after battling rheumatic heart disease.

North Island won 27–9 and following the match, which was part of a series of trials at Carlaw Park on the same day, Kirwan was selected in the New Zealand side to tour Australia.

[44] Kirwan scored a try in a 31–20 win over the Far North Coast side in Lismore before playing in the 20–29 loss to Queensland in Brisbane before a crowd of 10,000.

[46] [47] [48] The match with New South Wales was before a crowd of 15,000 at the Sydney Cricket Ground who saw Kirwan make a break and sent Jim Parkes in for a try which gave New Zealand the lead.

[52] In 1926 Kirwan played 8 matches for Marist scoring 5 tries though the key focus for the representative players this year was in gaining selection for the New Zealand tour to England.

[56][57] The tour stopped off in Fiji where during a training session Kirwan lost a large amount of skin from his wrist and elbow on the dirt fields there which was requiring daily treatment to heal.

He played in the tour opener against Dewsbury which was a 13–9 win on 11 September in front of 16,000, before appearing again against Halifax 7 days later with New Zealand losing 13–19.

[61] The selectors decided to rest captain Bert Avery and chose Kirwan to lead the side in their match with Salford on 3 November.

[62] Kirwan scored a try in an 8–10 loss against Huddersfield on 6 November before being selected to play in the centres against England in the second test at Hull.

He had earlier switched to the fullback position after Charles Gregory was injured and Kirwan's own injury occurred when he was tackling Sullivan as he scored.

[65][66] He missed the next two matches but with a large number of New Zealand's players on strike or injured by this point of the tour he was again selected to play against Pontypridd on Christmas Day.

Less than a month after arriving home from a rugby league season which had effectively lasted 9 months Kirwan was picked to play in a New Zealand team composed of the Auckland members of the touring side minus Kirwan's Marist teammate Arthur Singe who had been banned for life for his role in the strike on tour.