Mr Blair is expected to make at least part of the speech in French. If so, he will not be the first British Prime Minister to make a formal speech in France in French but he may be the first to do it well.
Those who have tried it before, with limited success, include Winston Churchill, Edward Heath and most recently, a heavily coached Margaret Thatcher at the opening of the Channel Tunnel works.
The French public has been astonished by the Prime Minister's command of their language in the brief television interviews he has given since he came to office last year. Mr Blair worked in France as a student and has spent several recent family holidays in the South-west of the country.
Although no final decision has been taken, officials in the French Parliament say they understand Mr Blair hopes to give part or all of his speech in French.
A date for the visit has yet to be finalised but it likely to be around 24 March.
Mr Blair will be only the fifth foreign head of state or government ever to address the National Assembly, the lower house of the French Parliament. His predecessors are King Juan Carlos of Spain, President Bill Clinton, King Hassan II of Morocco and the Italian Prime Minister, Romano Prodi. All but President Clinton spoke in French.
"This is a very new tradition for the assembly," said an official at the French Parliament yesterday. "No previous British prime minister has been invited because, until the last few years, we never invited heads of state or government to address us in this way."
The formal invitation to Mr Blair came from the former French Socialist Premier, Laurent Fabrus, who is now president of the assembly - something between the Speaker of the Commons and the Speaker of the US House of Representatives. The visit to Paris is also expected to include informal talks with the Socialist Prime Minister, Lionel Jospin, and the President Jacques Chirac.
Relations between Britain and France have been a little strained in recent weeks by the divergent approaches taken to the Iraq crisis. There have also been tensions on European issues, especially the exact nature of Britain's non-playing relationship with the countries who will join the Single European Currency next year.
Mr Blair and "Le Blairisme" retain a mostly positive image in France. The British Prime Minister is a favourite with French centre-right politicians and newspapers, if only as a stick with which to beat Mr Jospin and his more traditional approach to centre left politics.
In the last few weeks, however, there has been a re-examination of the adulation of Mr Blair. The left of centre news magazine Marianne devoted a column yesterday to Mr Blair's reported decision to block the House of Lords' attempt to end the Rupert Murdoch-inspired newspaper price war in Britain.
Marianne contrasted Mr Blair's "moralising" approach to politics with what it took to be his cynical decision to retain the support of the Sun.Reuse content