Hamdeen Sabahi, who came third in last year's presidential poll, has said he will stand again in elections expected in summer 2014.
In an interview on Tuesday with private satellite channel CBC, Sabbahi said political movements and parties would back one "revolutionary" candidate.
Sabbahi said he would prefer army chief Abdel-Fattah El-Sisi, who led the ouster of Mohamed Morsi, to stick to military matters, but he would respect political forces if they wanted him to stand for president.
Sabbahi had earlier said he would back a presidential bid by El-Sisi, who was a "popular hero."
Sabbahi's Egyptian Popular Current has already launched a campaign to promote Sabbahi as the "revolution's candidate."
Parliamentary and presidential elections are expected to take place by summer 2014, as detailed by the post-Morsi roadmap.
Sabbahi said he would vote Yes in an upcoming referendum on the amended constitution. "It's a better constitution [than 2012] but it's not perfect."
A veteran Nasserist and former MP, Sabbahi was jailed several times under Anwar Sadat and Hosni Mubarak.
The last time was in 2003, when his parliamentary immunity was lifted and he was jailed for organising demonstrations against the US-led war on Iraq.
He was a co-founder of the pro-democracy Kefaya (Enough) movement, which emerged in 2004 to oppose longtime autocrat Hosni Mubarak.
He is a leading member of the National Salvation Front, formed to oppose Mohamed Morsi.