Date Constituency Gain Loss Note
30 May 1963 Dublin North–East Fine Gael Fine Gael Paddy Belton (FG) holds the seat vacated by the death of his brother Jack Belton (FG)
27 October 1963 Dublin South–East Labour Party National Progressive Democrats Noël Browne (NPD) disbands the National Progressive Democrats and joins the Labour Party
27 October 1963 Roscommon Labour Party National Progressive Democrats Jack McQuillan (NPD) disbands the National Progressive Democrats and joins the Labour Party
27 October 1963 Dublin County Labour Party Independent Seán Dunne (Ind) joins the Labour Party
19 February 1964 Cork Borough Fianna Fáil Fianna Fáil Sheila Galvin (FF) wins the seat vacated by the death of her husband John Galvin (FF)
19 February 1964 Kildare Fianna Fáil Labour Party Terence Boylan (FF) wins the seat vacated by the death of William Norton (Lab)
8 July 1964 Roscommon Fine Gael Fine Gael Joan Burke (FG) holds the seat vacated by the death of her husband James Burke (FG)
3 December 1964 Galway East Fine Gael Clann na Talmhan John Donnellan (FG) wins the seat vacated by the death of his father Michael Donnellan (CnaT)
10 March 1965 Cork Mid Labour Party Labour Party Eileen Desmond (Lab) holds the seat vacated by the death of her husband Dan Desmond (Lab)