Niels Juel (8 May 1629 - 8 April 1697) was a Danish admiral.

Brother of diplomat Jens Juel, he was born at Christiania. He served his naval apprenticeship under Van Tromp and De Ruyter, taking part in all the chief engagements of the war of 1652-54 between England and Holland. During a long indisposition at Amsterdam in 1655-1656 he acquired a thorough knowledge of ship-building, and returned to Denmark in 1656 a thoroughly equipped seaman. He served with distinction during the Swedo-Danish Wars of 1658-60 and took a prominent part in the defence of Copenhagen against Charles X.

During fifteen years of peace, Juel, as admiral of the fleet, labored assiduously to develop and improve the Danish Navy, though he bitterly resented the setting over his head in 1663 of Cort Adelaar on his return from the Turkish wars. In 1661 Juel married Margrethe IJlfeldt. On the outbreak of the Scanian War he served at first under Adelaar, but on the death of the latter in November 1675 he was appointed to the supreme command.

He then won a European reputation, and raised Danish sea-power to unprecedented eminence, by the system of naval tactics, afterwards perfected by Horatio Nelson, which consists in cutting off a part of the enemys force and concentrating the whole attack on it. He first employed this maneuvre at the battle of Jasmund off Rugen (25 May 1676) when he broke through the enemy's line in close column and cut off five of their ships, which, however, nightfall prevented him from pursuing. Juel's operations were considerably hampered at this period by the overbearing conduct of his Dutch auxiliary, Philip Almonde , who falsely accused the Danish admiral of cowardice. A few days after the battle of Jasmund, Cornelius Van Tromp the younger, with 17 fresh Danish and Dutch ships of the line, superseded Juel in the supreme command.

Juel took a leading part in Van Tromp's great victory off Oland (1 June 1676), which enabled the Danes to invade Scania unopposed.

On the 1st of June 1677 Juel defeated the Swedish admiral Sjoblad off Moen ; on the 30th of June 1677 he won his greatest victory, in the Bay of Kjoge , where, with 25 ships of the line and 1267 guns, he routed the Swedish admiral Evert Horn with 36 ships of the line and 1800 guns. For this great triumph, the just reward of superior seamanship and strategy at an early stage of the engagement, Juel's experienced eye told him that the wind in the course of the day would shift from S.W. to W. and he took extraordinary risks accordingly; he was made lieutenant admiral general and a privy councillor. This victory, besides permanently crippling the Swedish navy, gave the Danes a self-confidence which enabled them to keep their Dutch allies in their proper place.

In the following year Van Tromp, whose highhandedness had become unbearable, was discharged by Christian V, who gave the supreme command to Juel. In the spring of 1678 Juel put to sea with 84 ships carrying 2,400 cannon, but as the Swedes were no longer strong enough to encounter such a formidable armament on the open sea, his operations were limited to blockading the Swedish ports and transporting troops to Rugen.

After the peace of Lund Juel showed himself an administrator and reformer of the first order, and under his energetic supervision the Danish navy ultimately reached imposing dimensions, especially after Juel became chief of the admiralty in 1683. Personally Juel was the noblest and most amiable of men, equally beloved and respected by his sailors, simple, straightforward and unpretentious in all his ways. During his latter years he was popularly known in Copenhagen as the "good old knight".

See Garde, Niels Juel (1842), and Den dansk. norske Smagts Hif tone, 5535-1700 (1861).