Bontempelli impressed scouts with his skills, athleticism, and leadership on the field, earning him a spot on the Western Bulldogs.

[15][16][17] There were talks of Essendon trying to obtain Bontempelli after it was stated they were prepared to send their eleventh selection and forward Stewart Crameri in exchange for pick four.

[19][20][21] Bontempelli made his senior debut in the Western Bulldogs's 28 point loss to Carlton in round 5 of the 2014 AFL season.

He received an AFL Rising Star nomination in round 13 for his 22 disposals and one goal performance in the Bulldogs' win over Collingwood.

[26] In round 15, Bontempelli kicked a remarkable goal tight up on the boundary in the final minutes of the match to give the Dogs a one-goal win over Melbourne.

[28] He finished second in the AFL Rising Star in the same year, losing to Brisbane Lions player Lewis Taylor by a single vote.

[30] Bontempelli polled 4 votes at the 2014 Brownlow Medal count that year, including three in his standout performance against Melbourne in round 15.

[34] In 2015 he picked up a career-high 28 disposals while playing Gold Coast, also kicking 2 goals, taking 7 marks and collecting 7 tackles.

[35] Bontempelli collected 24 disposals, 3 marks, 2 behinds and 7 tackles in the Western Bulldogs' seven point elimination final loss to Adelaide.

[32][43] Bontempelli had his best year yet in 2016, playing every single game of the season, including the Western Bulldogs fairytale premiership win.

[46] With the Bulldogs winning the match by eight points, Bontempelli became the youngest player in history to captain a VFL/AFL side to victory at 20 years and 194 days of age.

[54] He also made the All-Australian team for the first time, named on the interchange bench, alongside veteran teammate Matthew Boyd.

Bontempelli missed the 2017 JLT Community Series after a minor ankle injury at the club's pre-season camp in January.

[61] Former Melbourne and Sydney great Gerald Healy described Bontempelli as someone who 'could end his career as the greatest player in the history of the Western Bulldogs', after his 23 disposal, 2 goal performance against Brisbane Lions in round 20.

[70][71] However, he ended up playing his 100th AFL game in the Western Bulldogs's 44 point loss to Port Adelaide in round 19,[72][73] where he collected 22 disposals.

[74] Bontempelli broke his career high record for disposals twice in two consecutive matches in rounds 21 and 22, against Carlton and North Melbourne respectively.

[82] After questions as to why he only signed a shorter deal than expected, Bontempelli said "There's a bit of intrinsic value for me to continue to stay accountable to what I want to achieve.

I think his record and what he will do at the Western Bulldogs — I think he will captain the club and I think he will win a Brownlow — so give him another seven or eight years and we may be saying he was the greatest Dog there's ever been.

[96] Bontempelli tied with fellow Bulldog Jack Macrae to collect 22 votes in the 2019 Brownlow Medal,[97] judged best on field in 5 games—rounds 1, 3, 15, 19 and 20.

[98] Prior to the 2020 home-and-away season, he was selected to represent Victoria in the State of Origin for Bushfire Relief Match, played in February 2020.

[108] Bontempelli played his 150th AFL career game in round 5, where the Western Bulldogs strongly defeated Gold Coast.

[123][124] Bontempelli was credited with an "inspiring performance" to carry the Bulldogs to victory against Gold Coast in a tight game in Ballarat's round 10 match,[125] where he kicked 3 goals, 2 of those occurring in the last quarter.

[126] After the team's 17-point loss to Fremantle in round 21, Bontempelli suffered an adductor injury; however, the presence and extent of the injury was not fully understood by the football media and public until after Bontempelli's important performance in the penultimate round of the season,[127] where it was revealed by coach Luke Beveridge that despite some "niggles", he would be "raring to go" for the team's elimination final against Fremantle.

[128][129] Bontempelli finished fourth in the season for the Charles Sutton Medal, trailing leader Josh Dunkley by 57 votes.

[130] Bontempelli had an outstanding 2023 season, winning his fifth Charles Sutton Medal, placing second for the second time in the 2023 Brownlow Medal count (behind Lachie Neale), placing second for the AFL Coaches Association's AFL Champion Player Award (behind Zak Butters),[131] and called the best player of the year by sports journalist Mark Robinson.

[139] Known for his passionate activism on many social issues, Bontempelli was one of three AFL players who came together in 2015 to help advocate against violence towards women, alongside Shaun Burgoyne and Patrick Dangerfield.

[142] Chris Hemsworth starred as Bontempelli in an AFL advertising campaign that ran in the early months of 2017, in order to promote the game to international audiences.