His passion for the sea and probable aptitude for action rather than philosophical meditation interrupted his studies aged 14 when he began serving on the privateers that were common in the port of Dieppe.
A note from Toulon on his bearing stated "his manners are pure, exact in the service, inclined neither to wine nor gaming, good in political conduct, educated, with robust health, loved by his crew".
The Brune managed to draw off the British ships' fire, for which action general Martin promoted Deniéport to lieutenant de vaisseau on 21 germinal year IV (10 April 1796).
Deniéport then took part in a long campaign in the Levant and, when he came under suspicion from agents of the French Directory, the city of Sète attested to his loyalty.
Contre-amiral Perré wrote that Deniéport showed "conduct worthy of praise, a good officer, a true seaman, zealous, active, who very well fulfilled the several particular and very delicate tasks he was entrusted with".