Egyptian former intelligence chief Omar Suleiman will run for president, despite refusing to earlier this week.
He will now concentrate on getting the 30,000 signatures he needs before the deadline on Sunday.
The 74-year-old worked closely with ousted president Hosni Mubarak, briefly serving as vice president during the uprising.
Suleiman will be up against Muslim Brotherhood candidate and millionaire businessman Khairat al-Shater, who was mobbed by crowds of supporters in Cairo as he handed in his official papers on Thursday.
With the backing of the liberal Wafd party, former prime minister and head of the Arab League Amr Moussa represents the most popular secularist choice. He could be a counterweight in the Islamist-dominated parliament.
It is unclear whether Salafi Islamist Hazem Abu Ismail will be able to run.
His supporters demonstrated in Cairo’s Tahrir Square on Friday, claiming there is an official plot to stop him taking part.
Egyptian authorities say they are investigating if Ismail’s mother has a US passport – which would disqualify him from May’s presidential election.