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