Mohammed ElBaradei, the former head of the UN's atomic watchdog, has said he is to form what he called "a national association for change" in Egypt.
The announcement comes days after he returned to Egypt, and after he said he might run for president.
The association will not be the same as a political party, as the formation of parties is tightly controlled.
But Mr ElBaradei said anyone who wanted a change to the ruling party of President Hosni Mubarak could join him.
The announcement was made after holding talks with opposition figures and civil society leaders.
It's reported that a representative of the banned Islamist opposition movement the Muslim Brotherhood attended the meeting.
On Friday Mr ElBaradei was welcomed home after decades of living abroad by hundreds of people outside Cairo airport.
Magdi Abdelhadi, the BBC's Arab affairs analyst, says that for some Egyptians Mr ElBaradei's appeal lies in the fact that he is a civilian. Egypt has been ruled by the military since the monarchy was overthrown more than 50 years ago.
He has also been untainted by corruption allegations.
But detractors, writing in the state media, say that he is a figure who is out of touch with Egyptian life, having lived abroad for so many years.
Mr ElBaradei, 67, has built a strong reputation as head of the International Atomic Energy Agency (IAEA), winning the Nobel Peace Prize in 2005.
He stepped down in November and is now seen as the most credible potential challenger for the presidency.
He has said he might stand if there were reforms to guarantee a fair election and if he could run as an independent candidate. But for this to happen the constitution would have to be amended.
A campaign on the social networking website Facebook has become a focal point for those calling for Mr ElBaradei to run for the presidency.