Ashford was born in Birmingham, England in 1746 and arrived in Dublin, Ireland in 1764 at the age of eighteen. Within three years of his arrival, Ashford was exhibiting with the Society of Artists on William Street. At first, he was an amateur painter specializing in flower paintings and still life, but in 1772 he exhibited his first landscape at the Dublin Royal Society of Arts. He turned professional soon after. He spent a year in London (1789–90) where he became a member of the Society of Artists (London).
He was elected President of the Irish Society of Artists in 1813, was a founding member of the Royal Hibernian Academy, becoming its first elected President in 1823. In the early 19th century he painted a number of landscapes in and around Mount Merrion for Lord Fitzwilliam. It was near this time that he completed his Marino Casino, one of his finest works. Ashford was among the most respected landscape painters of Ireland in his time, on par with Thomas Roberts and George Barret. The architect, James Gandon, designed his home in Sandymount, County Dublin.
Most of his works were topographical views of country seats and well-ordered parks and his principal patrons were, therefore, the nobility and landowners. His painting, Landscape with Carriage and Horses, painted c.1781, is in the collection of the Ulster Museum.
There is a painting by William Ashford - "Belan House,County Kildare" - at the University of Michigan Art Museum in Ann Arbor.
There is also a painting by William Ashford, PRHA 1746-1824, "A Prospect of Belan House, County Kildare" - at BALLYFIN DEMESNE 
- "William Ashford". The Berger Collection. Retrieved 2008-07-11.[dead link]
-  William Ashford at Whyte's: Biographies or Irish Art and Irish Artists. Retrieved 22 March 2008.
- Arnold, Bruce. A Concise History of Irish Art. Thames and Hudson, London. 1969. pp. 91-92. Retrieved 21 April 2008.
- Aspects of Irish Art. National Gallery of Ireland. Cahill & Co. 1974. p. 106. Retrieved 22 March 2008.
- "William Ashford". Ulster Museum. Retrieved 2008-07-11.
- Ashford paintings donated to the Irish Heritage Trust
- Webb, Alfred (1878). " Ashford, William". A Compendium of Irish Biography. Dublin: M. H. Gill & son. Wikisource
- William Ashford (Encyclopedia of Irish and World Art)
- View of Killarney with the passage to the upper lake (1778 painting)
- The Casino at Marino, Dublin (1776 painting)
- A wooded landscape (n.d.)
- Landscape with Carriage and Horses (c. 1781 painting).