This is a list of singles which have reached number one on the Irish Singles Chart in 1975.
| Issue Date | Song | Artist |
|---|---|---|
| 2 January | Lonely This Christmas | Mud |
| 9 January | Lonely This Christmas | Mud |
| 16 January | Streets Of London | Ralph McTell |
| 23 January | Streets Of London | Ralph McTell |
| 30 January | Ms. Grace | The Tymes |
| 6 February | January | Pilot |
| 13 February | January | Pilot |
| 20 February | January | Pilot |
| 27 February | January | Pilot |
| 6 March | Make Me Smile (Come Up and See Me) | Steve Harley & Cockney Rebel |
| 13 March | Make Me Smile (Come Up And See Me | Steve Harley & Cockney Rebel |
| 20 March | If | Telly Savalas |
| 27 March | Bye Bye Baby | Bay City Rollers |
| 3 April | Bye Bye Baby | Bay City Rollers |
| 10 April | Bye Bye Baby | Bay City Rollers |
| 17 April | Bye Bye Baby | Bay City Rollers |
| 24 April | Love Is All | Red Hurley |
| 1 May | Love Is All | Red Hurley |
| 8 May | Oh Boy | Mud |
| 15 May | Oh Boy | Mud |
| 22 May | Oh Boy | Mud |
| 29 May | Stand By Your Man | Tammy Wynette |
| 5 June | Stand By Your Man | Tammy Wynette |
| 12 June | Stand By Your Man | Tammy Wynette |
| 19 June | Three Steps To Heaven | Showaddywaddy |
| 26 June | The Proud One | The Osmonds |
| 3 July | I'm Not in Love | 10cc |
| 10 July | I'm Not in Love | 10cc |
| 17 July | Tears on My Pillow | Johnny Nash |
| 24 July | Tears on My Pillow | Johnny Nash |
| 31 July | Give a Little Love | Bay City Rollers |
| 7 August | Give a Little Love | Bay City Rollers |
| 14 August | Barbados | Typically Tropical |
| 21 August | Barbados | Typically Tropical |
| 28 August | I Can't Give You Anything (But My Love) | The Stylistics |
| 4 September | I Can't Give You Anything (But My Love) | The Stylistics |
| 11 September | I Can't Give You Anything (But My Love) | The Stylistics |
| 18 September | Sailing | Rod Stewart |
| 25 September | Moonlighting | Leo Sayer |
| 2 October | Moonlighting | Leo Sayer |
| 9 October | Hold Me Close | David Essex |
| 16 October | Hold Me Close | David Essex |
| 23 October | Rhinestone Cowboy | Glen Campbell |
| 30 October | Rhinestone Cowboy | Glen Campbell |
| 6 November | Rhinestone Cowboy | Glen Campbell |
| 13 November | Rhinestone Cowboy | Glen Campbell |
| 20 November | Rhinestone Cowboy | Glen Campbell |
| 27 November | Rhinestone Cowboy | Glen Campbell |
| 4 December | Combine Harvester | Brendan Grace |
| 11 December | Imagine | John Lennon |
| 18 December | Bohemian Rhapsody | Queen |
| 25 December | Bohemian Rhapsody | Queen |
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