Elswick, Northumberland born inside left Jack Lavery began his football career with Jarrow Hibernians, playing for Hebburn Excelsior in 1902 and Northern Alliance club Jarrow in 1903, from where he was signed by Second Division club Barnsley that December, making his Football League debut at Woolwich Arsenal in February 1904. He played 4 matches for The Tykes before the season end, scoring twice, but returned to non league football with Midland League club Denaby United that summer.
Lavery returned to Football League action when he signed for Second Division club Leeds City in March 1906, as Leeds played their inaugural League season. He was given his debut in the goalless draw at Clapton Orient on 29th March and remained in the side at inside left through the final 8 matches, grabbing a couple of goals. After his performance against Gainsborough Trinity on 7th April, the Leeds Mercury reported: ‘The outstanding feature of the game was the fine display of Lavery, who filled the inside-left position for Leeds. In attacking work the little Denaby man was quite brilliant, while he showed an enterprise and a desire for work which were highly commendable.’ At 5ft 5½in tall, he is recorded as being the shortest player ever to feature in a senior team for Leeds City.
Lavery was a regular for Leeds throughout much of their 1906-07 campaign, scoring a hat-trick in a 6-1 win over Stockport County in December 1906, and played more than half their matches during 1907-08, but at the end of the campaign departed for Southern League club Swindon Town along with team mates Bob Jefferson and Harry Kay after 20 goals in 57 appearances for The Peacocks. He had two seasons with The Robins, scoring 16 goals in 46 matches, before signing for North Eastern League club South Shields Adelaide (now Gateshead) in 1910. He played for Hebburn Argyle later that year, his final recorded club before his eventual retirement.