As a teenager he studied sculpture at the École des Beaux-Arts under Louis Barrias and Charles Vital-Cornu and was represented at several exhibitions in Paris.

It was during one of these demonstrations on 8 July 1908 that he made the world's first flight with a lady passenger, his partner and fellow sculptor Thérèse Peltier.

In addition to his original Voisins airplane, he also bought three Blériot XIs, and formed a team by recruiting Hubert Le Blon, Léon Molon and Georges Prévoteau.

During 1909, Léon Delagrange participated in the following air race meetings:[2] Delagrange is known for his flight[7] at the First Flying Meeting in England, the Doncaster Aviation Meeting (18 and 26 October 1909[8][9]), where on the second and final day of the races (Tuesday, 26 October 1909), he flew his Gnome-engine Blériot XI monoplane on a one 6-mile lap in 7 minutes and 36 seconds (approximately 50–53 miles/hour), breaking the World record in spite of the infamously stormy weather[10][11] Delagrange was 4th in the Doncater Aviation competition program, which also included pilots such as Samuel Cody, Roger Sommer, Hubert Le Blon, Leon Molon, Walter Windham (the Aeroplane Club's founder), and Edward Mines.

[4] On 4 January 1910, in front of a crowd of spectators, he was piloting his Blériot XI as part of the Croix d'Hins over Bordeaux (France) in stormy weather, in an area whose winds frequently blew at the rate of 20 miles/hour.

Delagrange did not have time to disengage himself from his seat and was killed when the wreckage of his plane crashed to the ground and the motor crushed his skull.

The monoplane had been doubly-braced at the essential points and had been given a careful examination before ascending, with the accident attributed to the plane "maneuvering too quickly into the puffy wind".