His announcement, which officials say will be made during a televised address to the nation at 8 p.m. (1900 GMT), will mark the end of an era for France and clear the way for a new generation of younger politicians now vying for power.
Chirac, 74, has served as president since 1995 and leaves behind a difficult legacy for his successor, with the French economy underachieving most European peers, the state heavily indebted and social tensions simmering in deprived suburbs.
His natural heir in the conservative camp, presidential frontrunner Nicolas Sarkozy, said today he hoped to receive Chirac's endorsement, but also delivered a stern rebuke to his one-time mentor by promising a new approach to politics.
''I will not prevaricate with the French, I will not lie to them, I will not betray them,'' he said in an interview published in Le Journal du Dimanche newspaper.
''I want to be the candidate who says very clearly to the French what he will do if they give him their trust. That is my speciality.
I am therefore different from Jacques Chirac.'' Sarkozy is leading in the polls ahead of the April-May election, but he faces a tight race against his two main foes -- Socialist Segolene Royal and centrist Francois Bayrou.
Chirac, 74, has clung to the notion of possibly running again to avoid becoming a lame duck president, but a string of setbacks and a bout of ill health have left little doubt in most people's minds that he will not try to hold on to power.
LIGHT AND SHADE While in power, Chirac ended compulsory military service, stood firm against the increasingly popular far right and was the first president to acknowledge that France's Vichy regime had assisted the Nazis in the World War Two Holocaust.
He also played an important role in ending the civil war in Yugoslavia in the 1990s and won widespread popularity in the Arab world for standing up to US President George. W Bush over the invasion of Iraq in 2003.
But his attempts at reforming the French economy and tackling chronic unemployment met with little success and corruption scandals have dogged his time in office.
He also suffered some spectacular reverses -- notably in 2005 when the French rejected the European Union constitution in a referendum -- that diminished his domestic standing and weakened his position as a major international player.
''Overall ... it's seen as a very weak presidency, especially in the second term,'' said Daniela Schwarzer, an expert on France at the German Institute for International and Security Affairs.
Charismatic and clever, Chirac was brilliant on the campaign trail but had a less certain touch in office. At one point he had the worst popularity ratings of any French president, but his support has climbed as his retirement nears.
Chirac's mandate ends on May 17. After that, it is not clear if he will choose to play a continuing role in public life or withdraw to his rural retreat of Correze.
REUTERS SP PM1712