The boyband will release Greatest Hits on November 21 in the UK after celebrating a total of 14 number one singles and seven chart-topping albums.
A final tracklist for the collection is to be confirmed in the coming weeks, but fans of the group are able to pre-order the album now.
The standard edition will contain a string of Westlife classics as well as a couple of brand new tracks, while a two CD/DVD deluxe edition will also be available.
Speaking of the Greatest Hits release, the band said in a statement: "It's almost hard to believe that we've been doing this for as long as we have.
"We're incredibly proud of what we've achieved and are looking forward to releasing our Greatest Hits as a special thank you to our fans who have supported us throughout our career."
It will be the first release from the Irish act since they departed Simon Cowell's Syco record label earlier this year.
Since leaving the company, Westlife have revealed that they are happy about the decision to move to Sony RCA.
> Louis Walsh: 'No-one slags off Westlife'
Watch the music video for Westlife's number one single 'Flying Without Wings' below: