She announced a 100-point platform with a strong emphasis on social programmes, promising a higher minimum wage and the construction of more low-rent housing.
Ms Royal has been criticised for delaying the release of her platform until just 10 weeks before the first round of elections.
She has fallen behind her right-wing rival Nicolas Sarkozy in opinion polls.
Ms Royal unveiled her ""presidential pact"" in front of a cheering crowd of Socialist Party delegates who frequently broke into chants of ""Segolene, president!""
""I feel today I can propose to you something more than a platform,"" she said.
""A pact of honour, a presidential pact that I propose to everyone, the most vulnerable and the strong, those who have been our supporters all along and those who have not, because France needs all its people.""
Many of the 100 points already feature in the Socialist Party's election programme released last year.
Others, such as proposals to set up citizens' juries to evaluate the work of the National Assembly and military-style boot camps for young offenders are new ideas.
'Listening phase'
Ms Royal said she wanted to boost the monthly minimum wage from 1,250 euros ($1,625, ?834) to 1,500 euros, and build 120,000 low-rent homes every year.
Benefits for the unemployed would be raised and pensions increased for low-income retirees.
Ms Royal has defended her decision to delay the release of her manifesto, saying she had been in a ""listening phase"" - gathering ideas from the people of France via the internet and thousands of public meetings across the country.
Segolene Royal was France's political star of the second half of last year in France.
She had a meteoric rise thanks to her crowd-pleasing campaigning skills and trounced two more senior party figures in the Socialist domination for April's election.
But since the New Year things have begun to unravel, reports Hugh Schofield. There have been gaffes, signs of internal dissent and Nicolas Sarkozy has surged ahead in the polls.
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