[5] Weightman captained his school's first XVIII side at Haileybury, where he was coached by Australian Football Hall of Famer Matthew Lloyd.
[21] Weightman debuted in the Bulldogs' 42 point win over the Essendon Bombers in the 7th round of the 2020 AFL season, against friend and former teammate Ned Cahill.
He had a standout game in the VFL against Carlton's reserves side, where he took a spectacular mark over Ryley Stoddart[30] which grabbed the attention of seniors coach Luke Beveridge.
[34] The next week, Weightman was nominated for the 2021 AFL Rising Star award after his 2-goal, 14 disposal, 11 score-involvement performance against St Kilda.
[37][38] It was revealed Weightman had signed a two-year contract extension with the Western Bulldogs on 20 July 2021, tying him to the club until the end of the 2023 season.
[41][42] Weightman was one of the team's most important players in their 49-point elimination final victory over Essendon, kicking four goals to help them break away from the Bombers.
[43][44][45] After his 4-goal performance in the final, Weightman was subjected to abuse on social media platforms,[46] prompting teammate Josh Bruce to defend him on Twitter.
[49][50] Weightman played in the grand final, but had a quiet game as the Bulldogs ended up losing to Melbourne, picking up just seven disposals.