Mr Sarkozy has recently indicated he is considering a return to public office following his defeat in last year's presidential elections, amid polls suggesting French voters think he would do a better job of dealing with the country's economic woes than his successor Francois Hollande.
Downing Street declined to discuss the subjects expected to be discussed at this evening's meeting.
Mr Cameron's official spokesman told reporters: "They worked very closely together during Mr Sarkozy's time in office. During that time, they extablished a very strong working relationship.
"It is not unusual for prime ministers to meet former heads of government who they have worked very closely with."
Asked whether the meeting reflected an attempt by Mr Sarkozy to revive his political profile, the spokesman said: "The only thing it reflects is the nature of the relationship which they struck up while they were working together. It is a private meeting."
Mr Cameron developed a particular personal bond with Mr Sarkozy at the time of his father's death in 2010, when the then French president helped him return from a holiday in France in time to be at Ian Cameron's bedside in his final hours.
Mr Sarkozy, who is in London to address a client conference being held in private by merchant bank Goldman Sachs, has been the subject of increasing speculation about a possible future bid to return to the Elysee Palace.
The vice-president of France's opposition UMP party, Guillaume Peltier, has described him as "the right's natural leader" and is planning a Violet Rally next month to demonstrate the depth of support for his return.