Former Secretary of State for Wales Paul Murphy has urged the Welsh Labour leadership winner to include the other two contenders in their new cabinet.
The ballot to replace Rhodri Morgan closes at 1700 GMT, with the result announced on the evening of December 1.
The winner is due to become first minister and head of the Welsh Assembly Government around a week later.
Mr Murphy praised the conduct of Carwyn Jones, Edwina Hart and Huw Lewis throughout the two month campaign.
Ms Hart and Mr Jones are Health Minister and Counsel General respectively, Mr Lewis is AM for Merthyr Tydfil and Rhymney.
Welsh Labour members, local parties, affiliated groups, MPs, AMs and its MEP are eligible to vote, which can be done online until the deadline.