The unusually aggressive incident occurred as the president shook hands with a crowd in the town of Brax in southwest France.
The assailant was not armed, according to the national police service. An official with the service said the 32-year-old Frenchman lives in the Lot-et-Garonne region and works in the theater business. The official was not authorized to be publicly named due to police policy.
The man was detained and being questioned in the nearby town of Agen.
Images broadcast on French television showed Sarkozy reaching over a metal barricade to greet onlookers when an arm grabs his suit roughly by the shoulder and pulls it toward the crowd.
Sarkozy started to lose his balance and fall, then immediately recoiled and righted himself. Security officers pulled the assailant to the ground.
Sarkozy's office would not immediately comment on the incident. Sarkozy is an outspoken and divisive figure whose poll ratings have been quite low for months. He is expected to run for re-election next year, and his presidential visits to the French provinces in recent weeks have the air of campaign stops.
He occasionally gets heckled by critics, though only verbally. In one 2008 incident, a man was caught on video telling Sarkozy not to touch him as the president walked through a crowd.