Her father was Lance Samson, a newspaper editor and diplomatic correspondent for the Morning Star (died 4 February 2013) and her mother was a writer of Chinese descent, Esther Cheo Ying, who wrote a memoir, Black Country Girl in Red China, about her time serving as a Major in Mao Zedong's Red Army. Following a troubled childhood, Polly joined the publishing industry, through which she met the writer Heathcote Williams, with whom she had her first son, Charlie. Following his birth, Samson was left homeless by squatters and was taken in for a period by the journalist Cassandra Jardine.
Following their split, Samson met Pink Floyd singer and guitarist David Gilmour, whom she married in 1994 during Pink Floyd's Division Bell tour. They currently live in West Sussex. Her son Charlie was adopted by Gilmour and they have three other children: Joe, Gabriel, and Romany.
She has also written short stories for BBC Radio 4 and has had a collection published Lying in Bed (Virago 1999) and a novel, Out of the Picture (Virago 2000), as well as contributing pieces and stories to many other books and publications including Gas and Air (Bloomsbury 2003), Girls Night In (Harper Collins 2000), A Day in the Life (Black Swan 2003), and The Just When Stories (Beautiful Books 2010).