Colins was commissioned lieutenant on 2 November 1761.
During September 1769 he took the recommissioned schooner Magdalen out to Virginia from Portsmouth where she remained for the next six years. In June 1775 the Magdalen was threatened by the inhabitants of Williamsburg and a militia led by the prominent rebel Patrick Henry after the beleaguered governor of Virginia, Lord Dunmore, had ordered the removal of gunpowder from the local magazine. Colins was later obliged to evacuate the governor and Lady Dunmore down river to Yorktown.
By the autumn of 1776 he had succeeded the indisposed Captain George Montagu in command of the Fowey 24, and reaching Staten Island he took part in the landings on Manhattan during the New York campaign of July – October. Returning to England in December, the Fowey underwent a long refit before returning to New York in November 1777, during which period Colins had been promoted commander with effect from 23 August. The six-week passage took its toll however, with Colins being obliged to transfer over a third of his crew to hospital on her arrival, whilst on 21 November Captain John Henry was appointed to the command of the Fowey.
Later commanding the Zebra 14 from the spring of 1778, Colins was despatched by Vice-Admiral Lord Howe to watch for the arrival of the French Toulon fleet on the American coast, and after bringing in news of their approach he commanded her at the defence of New York in July. At the end of September he took the Zebra out of New York with fifteen other small vessels in what became known as the Egg Harbour Expedition and proceeded to Chestnut Neck where he ordered the destruction of the town and ten vessels on 6 October. Following the arrival of rebel artillery he decided to abandon any further advancement, but with the ships being unable to re-cross the bar the Zebra was abandoned in Little Egg Harbour on the 21st, being fired and blown up the next day.
Colins was posted captain on 20 March 1779 and he commanded the Victory 100 as the flagship of Admiral Sir Charles Hardy in the Channel from 28 March, taking part in the retreat of August 1779. Removing from the Victory on 12 May 1780, he was appointed to the Aurora 28 later in the year in which he captured the privateer Esp rance 10 off Lands End on 23 April 1781 and the Comte de Guichen 18 on 4 May, prior to leaving his command in the same month. He next joined the Aeolus 32 in February 1782, capturing the privateer Agla 20 off Cornwall on 18th April whilst sailing for Newfoundland. She was eventually paid off in April 1783.
Colins commanded the Culloden 74 from 1789-91, being attached to the Grand Fleet during the Spanish Armament on 1790, and going out to the Leeward Islands with Rear-Admiral Samuel Pitchford Cornish at the end of the year before coming home to be paid off in March 1791.