Baghdad officials said former Education Minister Khudayr al-Khuzai joins Adel Abdul Mahdi and Tariq Hashemi as deputies serving under Iraqi President Jalal Talabani, al-Arabiya reports.
The number of deputies under Talabani was a sticking point to forming a unity government following months of political wrangling last year.
Former interim Prime Minister Iyad Allawi won a March 2010 parliamentary contest but wasn't able to secure the political majority needed to take over for Iraqi Prime Minister Nouri al-Maliki.
Both leaders remain at loggerheads as Maliki struggles to fill top positions in his Cabinet with new members. Allawi complains Maliki is exerting too much control over the political process and Maliki in April threatened to dissolve the government in 100 days if political rows continued.
Mahdi is a Shiite member of the Supreme Iraqi Islamic Council while Khuzai is a member of Maliki's State of Law party. Hashemi is from Allawi's party, Iraqiya.