Gwendolen Florence Mary Guinness, Countess of Iveagh (née Onslow; 22 July 1881 – 16 February 1966) was an Anglo-Irish aristocrat and Conservative politician.

She was married to the Conservative Member of Parliament (MP) for Southend, Rupert Guinness, 2nd Earl of Iveagh.

The Countess of Iveagh, as Gwendolen Guinness was now known, won the Southend by-election on 19 November 1927 to replace her husband as MP.

When she retired in 1935, she was succeeded as MP by Henry "Chips" Channon, the husband of her eldest daughter, Honor Guinness.

[2] In 1956 she presented her Surrey childhood home, Clandon Park House, to the National Trust.