Ayman Nour has received an official pardon from the Supreme Council of the Armed Forces (SCAF) and intends to run for the presidency, he announced on his official Twitter account Wednesday.
Nour had been banned from politics since being convicted of forging signatures to secure the formation of the liberal Al-Ghad Party in 2005.
The charges, which Nour described as "trumped up," were widely seen as a reaction to his campaign against Mubarak in the 2005 presidential election. He finished a distant second with 540,405 votes.
Nour was released from prison in 2009 for health reasons after serving more than four years.
However, the conviction, which banned him from running for any political office for at least five years after the end of his jail term, remained in place.
In 2011 he made a failed attempted to overturn the conviction, arguing that he had been wrongly convicted.
To run, Nour requires either 30,000 recommendations from 15 different governorates, recommendations from 30 different MPs or to be registered as a party candidate before 8 April.
Nour is a founder of the liberal Ghad Al-Thawra Party which he formed in 2011 after a number of internal disputes with the Al-Ghad Party.
Ghad Al-Thawra won two seats in recent parliamentary elections as part of the Muslim Brotherhood's alliance.
Egypt's presidential elections are to take place on 23 and 24 May.