For the 2024-2025 session, the 18th legislative district of the New Jersey Legislature is represented in the State Senate by Patrick J. Diegnan (D, South Plainfield) and in the General Assembly by Robert Karabinchak (D, Edison) and Sterley Stanley (D, East Brunswick).

Since the creation of the 40-district legislative map in 1973, the 18th district has always been centered around central Middlesex County and has always included East Brunswick, Edison, and Metuchen in every decennial redistricting.

[13] Derman and Warsh won re-election in 1993, defeating former Assemblymember Thomas H. Paterniti and his running mate Matthew Vaughn.

[16] In the 1995 elections, the Assembly seats swung back to the Democrats, with Barbara Buono holding onto her seat and her running mate Peter J. Barnes Jr. winning too, defeating Republican incumbent Warsh and his running mate Jane Tousman, despite Republicans outspending the Democrats by a 2-1 margin in the bitterly fought battleground district.

[24] In the 18th district, Peter J. Barnes III moved from the Assembly to the Senate, winning Buono's seat against East Brunswick mayor David Stahl in a close race.

On May 5, Diegnan was selected without opposition to receive an appointment to the Senate seat by the members of the Middlesex County Democratic Organization.

A week later, on May 12, Edison Councilman Robert Karabinchak was selected from a ballot of four candidates to receive appointment to Diegnan's Assembly seat.