Simplify the following text for a Grade 11 native English-speaking person.
Original: On 10 July 1917 he was elected member of the British House of Commons for East Clare ( the constituency which he represented in Dail Eireann until 1959 ) in a by-election after MP Willie Redmond died fighting in World War I.
Simplified: On 10 July 1917 he was elected member of the House of Commons for East Clare ( the constituency which he represented until 1959 ) in a by-election caused by the death of the previous incumbent Willie Redmond , brother of the Irish Party Leader John Redmond who had died fighting in World War I. In the 1918 general election he was elected both for that seat and Mayo East .