Endeavour was originally the merchant collier Earl of Pembroke , built by Thomas Fishburn for Thomas Millner, launched in June 1764 from the coal and whaling port of Whitby in the North Riding of Yorkshire. She was a type known locally as the ‘Whitby Cat’. She was ship-rigged and sturdily built with a broad, flat bow, a square stern, and a long box-like body with a deep hold.

A flat-bottomed design made her well-suited to sailing in shallow waters and allowed her to be beached for loading and unloading of cargo and for basic repairs without requiring a dry dock. Her hull, internal floors, and futtocks were built from traditional white oak, her keel and stern post from elm, and her masts from pine and fir. Plans of the ship also show a double keelson to lock the keel, floors and frames in place.

There is uncertainty about the height of her standing masts, as surviving diagrams of Endeavour depict the body of the vessel only, and not the mast plan. While her main and foremast standing spars were standard for her shipyard and era,^[16] an annotation on one surviving ship plan in the National Maritime Museum in Greenwich has the mizzen as “16 yards 29 inches” (15.4 m). If correct, this would produce an oddly truncated mast a full 9 feet (2.7 m) shorter than the naval standards of the day. Late twentieth-century research suggests the annotation may be a transcription error with “19 yards 29 inches” (18.1 m) being the true reading. If so, this would more closely conform with both naval standards and the lengths of the other masts.^[15