Miriam Escofet, who graduated in 3D design from what was then known as Brighton Art School in 1990, scooped the BP Portrait Award at a ceremony at the National Portrait Gallery in London.
Miriam was presented with the prize by model and actor Lily Cole.
The artist’s winning painting – which depicts her mother drinking tea in her kitchen – is entitled An Angel At My Table.
It won plaudits from the judging panel for its “constraint and intimacy” and “surreal quality”.
One of the judges, Rosie Millard, said of the painting: “The crisp tablecloth and china are rendered so beautifully and then you see that one of the plates and a winged sculpture on the table appear to be moving, which adds a surreal quality to the portrait.”
Sam Davies, the university’s Director of Philanthropy and Alumni Engagement, said: “Congratulations to Miriam and we hope we will be able to welcome her back to the campus in due course.
“It would be wonderful to expose our current students to an artist of Miriam’s calibre as they look towards their own careers.”