Newcastle-born Willie Ferguson Macdonald, the son of a tailor, was apprenticed initially to James Watson at Belle Isle, Yorkshire, before

 -  three years later - joining J. R. Humphreys at Lambourn.

He rode his first winner, Tetrarch, at Sandown on April 27, 1876.

William won his second Cesarewitch in 1881 on Foxhall

William's first big win came on Ivy in the Ayr Gold Cup on Friday 21 September 1877

William's first Cesarewitch victory, on Tuesday 7 October, 1879, came aboard the three-year-old Chippendale, a brown colt by Rococo out of Adversity by Adventurer, foaled in 1876.  

Earlier that same season, on Friday, 13 June, Chippendale had taken the inaugural running of the Hardwicke Stakes at Ascot under John Osborne Jr. 

William's brother, James (1856 - 1888), was also a jockey.

William Macdonald died at the Sefton Arms Hotel, Aintree, in the early hours of Saturday, 12 November, having never truly recovered from the injuries he sustained when brought down by a stray dog during the Liverpool Autumn Cup. There had been a brief cause for hope on the Friday morning, when he rallied sufficiently to regain consciousness and take some beef tea, but a relapse followed and he died at around half-past five, despite every medical assistance being rendered. At an inquest held on Monday, 14 November, a verdict of accidental death was returned. 

Before his death, he had ridden 29 winners that season. The previous year, 1880, had been particularly successful — he rode 40 winners, among them Zealot, carrying him to victory in the Prince of Wales's Stakes. It was also on Zealot that he had made his maiden Epsom Derby mount a fortnight before that win. This year's Derby had seen him ride Limestone. 

William's early career was closely bound to Tetrarch, the horse on which he rode his first winner and went on to claim the 1876 Great Shropshire. It was also Tetrarch who was responsible for his first serious setback: at Aintree in 1877, during the Great Lancashire Handicap, the horse stumbled and fell, throwing William and breaking his collarbone. What could not have been known at the time was that the spot where he lay injured was the very same stretch of course where, four years later, he would fall fatally from Buchanan.