He was the aide-de-camp of Marshal Maurice de Saxe and visited St. Petersburg in that officer's interest in 1741.

He was sent to Canada on 20 February 1755 as the head of French troops to conduct the campaign against the British.

[1] After pursuing their opponents to the British camp, the Indians halted; the Canadians became alarmed; and Dieskau, with his 200 regulars, was forced to sustain the fight.

Almost all the French regulars perished [dubious – discuss] [citation needed], and Dieskau himself was wounded three times but refused to retire and seated himself on a stump exposed to the bullets.

Finally, seeing a soldier approaching as if to capture him, Dieskau put his hand into his pocket for his watch, which he intended to give to his captor, but the man, supposing that he was drawing a pistol, shot him and inflicted a wound that ultimately caused Dieskau's death over a decade later.