Makhdoom Shahabuddin on Thursday lodged his bid to be elected prime minister by parliament, in a move expected to end a power vacuum created by the dismissal of premier Yousuf Raza Gilani for contempt.
A consensus choice and a loyalist, Shahabuddin was briefly finance minister during the 1993-1996 premiership of Benazir Bhutto, Zardari's wife who was assassinated in 2007.
His nomination was announced after more than 24 hours of crisis talks and intense horse trading between Zardari and members of his fractious ruling coalition.
In brief remarks at the national assembly, Shahabuddin showcased his loyalty by thanking Zardari and extending greetings to members of the main ruling Pakistan People's Party (PPP) on the birthday of his late wife.
"I am thankful from the bottom of my heart (to Zardari)," he told reporters.
"Today is a special day because it is Benazir Bhutto's birthday and I send my congratulations on this birthday to all party workers," he added.
A second PPP "cover" candidate, Raja Pervez Ashraf, also lodged his nomination papers and the lower house of parliament will now meet Friday to elect the new prime minister.
The main opposition party led by former prime minister Nawaz Sharif also announced it will field a candidate in what is likely to be a symbolic move as the PPP leads a majority in the assembly.
"We will contest the election for the new prime minister and Sardar Mehtab Ahmad Khan will be our candidate," Siddiqul Farooq, a PML(N) spokesman told AFP.
Khan is former chief minister of the Khyber Pakhtunkhwa province and an MP from the northwestern Abbottabad city.
Gilani, who became prime minister after the PPP won elections in 2008 ending nearly a decade of military rule, was dismissed after being convicted of contempt for refusing to ask Swiss authorities to reopen corruption cases against Zardari.
Gilani always insisted Zardari had immunity as head of state and that writing to the Swiss would be a violation of Pakistan’s constitution.
The cases against Zardari date to the 1990s, when he and Bhutto are suspected of using Swiss banks to launder $12 million allegedly paid in bribes by companies seeking customs contracts.
The Swiss shelved the cases in 2008 when Zardari became president.