The polls were called following the deaths of Middlesbrough Councillors Bernie Taylor and Peter Cox.
The long-serving ward members represented Ayresome and Park End & Beckfield wards respectively.
By-elections will take place on Thursday, July 13 between 7am and 10pm.
Candidates as follows:
Jill Coleman Conservative Party
Carl Martinez Green Party
Rhid Nugent Liberal Democrats
Vic Walkington Labour Party
Park End & Beckfield Ward
Ron Armstrong Conservative Party
Ian Blades Labour Party
Wen Cai Bowman Liberal Democrats
Jan Mohan Independent
Jamie Rawlings Green Party