He was the son of Alexander Lvovich Naryshkin and his wife Maria Alexeyevna Senyavina, daughter of Admiral Alexei Senyavin.
This made Lev brother to Elena Aleksandrovna Naryshkina and first cousin to Prince Mikhail Semyonovich Vorontsov, who fought in the Napoleonic Wars and the conquest of the Caucasus.
He fought at Gutstadt, Heilsberg and Friedland, where he was wounded in the arm and decorated with a gold sabre.
The French invasion of Russia forced Naryshkin back into the army as a cavalry captain in the 11th Izyumovsky Hussars Regiment, and he faced the Grande Armée at the battle of Ostrovno, near Smolensk, on 25 and 26 July 1812, then at Borodino, where he was wounded in the head.
He was freed by Cossacks near Vitebsk and rejoined his regiment, in which he became colonel on 19 November 1812, in recognition of his bravery at Berezina.