She is described as a "brown-haired woman with a pale face and very deep set grey eyes". Reverend Clement initially thinks of her as "a quiet, self-contained woman whom one would not suspect of any great depths of feeling". However, after he discovers that she is having an affair with Lawrence Redding, he realises that she is a desperate woman.
On the day of the murder, Anne tells Miss Marple that she is calling at the vicarage for her husband. Miss Marple sees her turn round the corner of the house, come back almost immediately, and go to the shed, which Lawrence Redding uses as a studio.
Anne confesses to killing her husband, saying that she had hated him for a long time. She claims that she got her husband's gun out of his drawer, brought it to the vicarage, and shot him. However, Miss Marple says that this is not true, as Anne did not have a gun with her, and had no way of concealing one on her person.
It is later revealed that Anne did indeed shoot her husband. Lawrence Redding had earlier visited the vicarage, and left his gun concealed in a potted plant near the window. After talking to Miss Marple, Anne went to the study, took the gun from the pot, and shot her husband from behind. She then threw the gun down, left the study, and went to the studio to meet Lawrence.
Miss Marple recollects her actions in The Mirror Crack'd from Side to Side.
In the BBC 1986 adaptation of the novel which formed part of the Miss Marple series, Anne Protheroe is played by Polly Adams. The name is changed slightly to "Ann". Unlike in the novel where she was tried for murder, here she took her own life.
In the ITV 2004 adaptation of the novel (Episode 2, Season 1 of Agatha Christie's Marple), Anne is played by Janet MacTeer. The portrayal is slightly more sympathetic than in the original novel. She is a personal friend of Miss Marple and she tells her that years before, she had loved Lawrence Redding but he had gone off to war and had been posted as missing. Years after the war, she read of an artist who had made a comeback on the London scene and found out that it was Lawrence, but by then she had already married Protheroe. She sought out Lawrence and persuaded him to live at St. Mary Mead. Her discussion of what might have been led Miss Marple to have flashbacks about a time when she had loved a married soldier named Captain Ainsworth.