Celia Montague, pictured, who appeared in an episode alongside Sir John Gielgud and Robert Hardy, persuaded the writer to sit for a portrait for the first time.
Both artist and author were delighted with the result, with the painting on show at St Barnabas Church in Jericho until Monday.
The actress turned artist, who lives in Norham Road, Oxford, asked Mr Dexter if he would sit for her when they met in Oxford Town Hall in March, where the writer was opening an exhibition.
Ms Montague said: “I thought it would be an amusing idea for one of his characters to paint Morse’s creator and happily he thought it would be amusing too. He sat for me at his home in Oxford. There were five sittings, each about three hours. He is a kind and humorous person.
“He likes the portrait very much. He became quite protective of it. When I drove away with it in my red van he called out, ‘Mind what you are doing with that painting’.”
With an actresses’s perfect sense of timing she completed it just in time for it to be featured in an exhibition in the Jericho church, where 19 of her paintings are on show.
She said: “It was framed on the day the exhibition opened.”