[1] The seat became vacant after the sudden death of the incumbent assemblyman and Selangor state executive councillor, Shaharuddin Badaruddin on 2 August 2018 from colon cancer.

Shaharuddin won the seat with a majority of 19,372 votes, defeating BN's Yusoff M Haniff, PAS's Mohd Ghazali Daud and independent S Vigneswaran.

In opposite to the Sungai Kandis and Balakong by-elections, the Barisan Nasional (BN) decided not to contest in Seri Setia.

The by-election campaign largely focused on bread and butter issues, such as local development and the introduction of a new sales tax replacing the GST.

The PAS candidate Halimah claimed that Seri Setia was too "intelligent" to vote for "local boy with an outdated mentality", insinuating about her opponent's poor origins.