Her father was well connected to artists and had his daughters painted by both Sean Keating and Tom Ryan (b.1929) who was the artist here.
The sale came about as O'Connor wanted to raise awareness and funds to support the The Penny Dinners, an old Dublin charity providing for the needy, and it was one of two pictures which she put into the auction.
The 23 x 19in (57 x 48cm) pastel on tinted paper was signed by both artist and the sitter (long before she adopted her trademark shaved head hairstyle) and was dated November 1974.
Estimated at €5000-7000, it was knocked down at €8500 (£7205).
The other work was Upon Small Shoulders, a large oil on canvas painted last year by Neil Condron (b.1956), which is due to feature in the singer's forthcoming autobiography. It sold at €19,500 (£16,525).
The auctioneers also donated their fees to the charity.