[5] Since his election, Mullahy has overseen and advocated for major investment into the Glen Waverley District, including in schools, open space and the Suburban Rail Loop.

[citation needed] Upon Matt Fregon's surprise victory at the 2018 Victorian State Election, Mullahy decided to work full time as an electorate officer, providing constituency services to the then Mount Waverley District.

Mullahy won Glen Waverley following an 8% collapse in the Liberal primary vote, and a 4% swing to Labor, on a two-party preferred basis.

[11] Mullahy advocated for the Andrews Government's dedicated public elective surgical centre in Blackburn and the expansion of free, extended hours Priority Primary Care Clinics into his electorate.

[12] Both during the election campaign, and in his term as Member of the Victorian Legislative Assembly, John has been actively supportive of the Suburban Rail Loop, which will connect Glen Waverley Station with employment, education and health precincts across Melbourne.