na June 1998, Byrne gara nyocha maka otu nwa okorobịa Irish ọhụrụ, ebe onye njikwa Boyzone bụ Louis Walsh bịakwutere ya ka ọ sonyere ya na ọrụ ọhụrụ ya, Westlife. Byrne sonyeere Westlife yana Kian Egan, Mark Feehily, Shane Filan na Brian McFadden. Byrne kpughere na Westlife: Akụkọ anyị na ọ chọrọ ịgbanwe aha otu ahụ na West High; mana ndị ọzọ họọrọ Westlife. Na Westlife, Byrne nwere 25 UK iri kacha elu, 14 n'ime ha, bụ nọmba otu, 7 nọmba otu albums ma rere ihe karịrị 55 nde ihe ndekọ n'ụwa nile. A kwadoro na Westlife erewo nde 20.2 na vidiyo na UK n'oge ọrụ afọ 14 ha <unk> 6.8 nde, nde 11.9 na nde 1.5 vidiyo. Byrne nwekwara otu nọmba otu na Ireland na 2002, n'akụkụ Republic of Ireland football team na 2002 FIFA World Cup.
Kian Egan, Mark Feehily, Shane Filan na Brian McFadden