Before their success, the band served as supporting opening acts for the boy bands Backstreet Boys and Boyzone. Since then, the group has recorded studio and live performances with music acts including Mariah Carey ("Against All Odds (Take a Look at Me Now)"), Lulu ("Back at One"), Joanne Hindley ("The Way You Look Tonight"), Diana Ross ("When You Tell Me That You Love Me"), Donna Summer ("No More Tears (Enough Is Enough)"), and Delta Goodrem ("All Out of Love"), "If I Had Words" with The Vard Sisters, "I Have A Dream" with Indonesian child-star Sherina. These songs were also recorded and included on various albums. In 2002, Westlife re-recorded their hit song "Flying Without Wings" with Mexican singer Cristian Castro and with Korean singer BoA as two separate duets.
Westlife has performed live duets with many other music artists including: Will Smith, Wyclef Jean, Toby Keith, Esperanza Spalding, Luis Fonsi, Alexander Rybak, Amadou and Mariam, Willow Smith, Jaden Smith, Jada Pinkett Smith, Lang Lang, Natasha Bedingfield ("Man in the Mirror"), Wang Leehom ("You Raise Me Up"), Mary Black ("Walking in the Air"), Sinéad O'Connor ("Silent Night"), Dean Verbeeck ("Swear It Again"), Donny Osmond ("Crazy Horses"), Kevin Spacey ("Beyond the Sea"), Mariah Carey ("Never Too Far/Hero Medley"), Secret Garden ("You Raise Me Up"), Lionel Richie ("Easy"), Boyzone ("No Matter What"), Ronan Keating ("The Dance"), Ray Quinn ("That's Life"), JLS ("Flying Without Wings"), Dolores O'Riordan of The Cranberries ("Little Drummer Boy") and various artists for a charity single and live concert or television performances with music artists such as Steps, 5ive, S Club 7, Blazin' Squad, Gareth Gates, Liberty X, Girls Aloud, Busted, McFly, Emma Bunton, Leona Lewis, Rod Stewart, Cheryl, Mika, Michael Bublé, Joe McElderry, Miley Cyrus, James Blunt, Blue, Gary Barlow, Mark Owen, Jon Bon Jovi, James Morrison, Alexandra Burke, Jason Orange, Susan Boyle, Rachel Stevens, JLS, Jamie Cullum, Gloria Estefan, Kylie Minogue, Robbie Williams, and V, where the former boyfriend of Feehily was a member named Kevin McDaid. In 2018, the band is reported to have a collaboration with Ed Sheeran for their comeback single.