The following is a list of the IRMAs number-one singles of 1989.
| Issue Date | Song | Artist | Ref. |
|---|---|---|---|
| 5 January | "Especially for You" | Kylie Minogue and Jason Donovan | |
| 12 January | |||
| 19 January | |||
| 26 January | "The Living Years" | Mike + The Mechanics | |
| 2 February | "Something's Gotten Hold of My Heart" | Marc Almond featuring Gene Pitney | |
| 9 February | |||
| 16 February | "Belfast Child" | Simple Minds | |
| 23 February | |||
| 2 March | "Leave Me Alone" | Michael Jackson | |
| 9 March | "Too Many Broken Hearts" | Jason Donovan | |
| 16 March | "Like a Prayer" | Madonna | |
| 23 March | |||
| 30 March | "Paradise City" | Guns N' Roses | |
| 6 April | "Eternal Flame" | The Bangles | |
| 13 April | "When Love Comes to Town" | ||
| 20 April | "Eternal Flame" | The Bangles | |
| 27 April | |||
| 4 May | "Far from Home" | Daniel O'Donnell | |
| 11 May | "Hand on Your Heart" | Kylie Minogue | |
| 18 May | "Ferry Cross the Mersey" | Gerry Marsden, Holly Johnson, Paul McCartney & The Christians | |
| 25 May | |||
| 1 June | "Heart & Soul" | No Sweat | |
| 8 June | |||
| 15 June | "Sealed With a Kiss" | Jason Donovan | |
| 22 June | "All I Want Is You" | U2 | |
| 29 June | |||
| 6 July | "And a Bang on the Ear" | The Waterboys | [1] |
| 13 July | "Liberian Girl" | Michael Jackson | |
| 20 July | "You'll Never Stop Me Loving You" | Sonia | |
| 27 July | "Too Much" | ||
| 3 August | |||
| 10 August | "Swing the Mood" | Jive Bunny and the Mastermixers | |
| 17 August | |||
| 24 August | "Lion in a Cage" | Dolores Keane | |
| 31 August | |||
| 7 September | "Every Day (I Love You More)" | Jason Donovan | |
| 14 September | |||
| 21 September | "Right Here Waiting" | Richard Marx | |
| 28 September | "Ride on Time" | Black Box | |
| 5 October | "Sweet Surrender" | Wet Wet Wet | |
| 12 October | |||
| 19 October | "That's What I Like" | Jive Bunny and the Mastermixers | |
| 26 October | |||
| 2 November | |||
| 9 November | "Never Too Late" | Kylie Minogue | |
| 16 November | "Don't Know Much" | Linda Ronstadt & Aaron Neville | |
| 23 November | |||
| 30 November | |||
| 7 December | "When You Come Back to Me" | Jason Donovan | |
| 14 December | "Do They Know It's Christmas?" | Band Aid II | |
| 21 December | |||
| 28 December |