Ridsdale was educated at University College School and the Royal School of Mines. He served as Member of Parliament for Brighton from 1906 to 1910, when he did not stand for re-election after disagreeing with government policy. He was chairman of the Executive Committee of the British Red Cross Society from 1912 and 1914 and deputy chairman from 1914 to 1919. In recognition of this work during the First World War he was knighted as Knight Grand Cross of the Order of the British Empire (GBE) in the 1920 civilian war honours.
He was a Fellow of the Geographical Society.