Westlife's debut album and single coincided with the apogee of boy band popularity, and their success was most apparent in their homeland, the UK, and most of African, Asian, Australian and European countries. They had 12 worldwide concert tours over their 14-year career. On April 2001, over one million fans wanted to chat with the lads from 122 countries. They have more than 50,000 official fans club members in mainland China alone in 2006. Boy band One Direction was mistaken for Westlife in Ghana. Three of their studio albums were part of the 50 fastest selling albums of all time in UK. In 2000s, Swear It Again became a popular song for wedding and funerals in the British Isles. In 2009, Flying Without Wings was listed as seventh most popular song for wedding's first dances in UK. In 2016, three of their songs (I'll See You Again, Flying Without Wings, You Raise Me Up) made it on the top pop music choices for funerals in Ireland. They are Vietnam's most viewed music artist in YouTube as of 2015. In South Korea, their singles "My Love" and "You Raise Me Up" stayed in the top 60 of the Official International Karaoke Charts since the inception of the charts in December 2010 up to its recent chart released. They are the biggest selling international, foreign album act in Philippine and Indonesian music records history.

They were invited by Wayne Rooney and Coleen Rooney to sing on their wedding reception in Portofi no, Abbey of Cervara, Italy and got paid £400,000, one of the highest amount paid acts for a wedding. They are Coleen's favorite pop band, invited to Coleen's 21st birthday but was unable to make it. The band also performed for the Sultan of Brunei, an occasion on which they were paid £2.5 million to play a private concert of seven songs. They also performed at the Nobel Peace Prize Concert in 2000, and in 2005 with the songs "World of Our Own" and "You Raise Me Up" with Rolf Løvland and Fionnuala Sherry, and in 2009 with "What About Now" and "You Raise Me Up" in front of former US President Barack Obama and met him afterwards. They also played for Pope John Paul II and Queen Elizabeth II in a live concert television show and shook hands with them. They were the first ever pop band to top the entertainment bill at the Vatican and a private concert for the Pope. They also personally met former UK Prime Minister Tony Blair and picked autographs also for his daughter. The band was also mentioned in the book version of Me Before You, which was released in 2012.

Despite their success worldwide, Westlife was unable to break into the U.S. market. They had only one hit single in the United States, "Swear It Again", which peaked at number 20 on the Billboard Hot 100 in 2000. The band made an appearance on MTV's Total Request Live and the U.S. edition of their debut album, Westlife was released, but it didn't meet with success. In 2002, with the two most prominent boy bands in the US, the Backstreet Boys and *NSYNC, going on hiatus that year, an attempt was made to promote and release a US version of World of Our Own, but was never successful. Billboard called the failure due to corporate politics.

"We sent over a CD of World of Our Own with no name on it. They didn't know it was Westlife and every single radio station in the States – all came back and said that this is an absolutely huge hit. They said it was great for radio and people are gonna love it, especially as there's just a slight bit of rock guitar to it. But as soon as we revealed it was Westlife, the radio pluggers all went, 'Whoa, not Westlife – it's a boyband.' And we cannot break that down, no matter what song we come out with. The problem with America is that it's all radio and you've got to break into radio first. And currently radio doesn't want to play boy bands or pop music. If Bono wrote a song with us tomorrow and it was the biggest hit in the world, if Westlife's name is put to it, it won't be a hit in America because radio will not play us."

— Nicky Byrne

"Flying Without Wings" peaked at No.2 in the USA when American Idol Season 2 winner Ruben Studdard recorded and released it as his debut single. In 2003, Westlife went to Nashville to film a TV documentary. While they were there, they gave a live performance of the song "Daytime Friends", originally by country music singer Kenny Rogers. Though Westlife didn't gain as much success in the States as they did elsewhere, their music was still appreciated. Kid David Corey, assistant PD and music director at top 40 WXKS (Kiss 108) radio station in Boston, Massachusetts was a Westlife supporter that was recorded saying "Bands like Backstreet Boys and 'N Sync are still climbing the charts, and radio is supporting them, so I don't think the boy band thing is going to hurt them. Besides, this song ["Swear it Again"] is just too good for any of that to be a concern. I can't imagine anyone not playing this because it's another boy band, especially when it doesn't even sound like those other guys."

Celebrities including Chris Martin of Coldplay, Jamie Vardy, Elton John, Sharon Osbourne, Martine McCutcheon, Niall Horan, Neil Murillo, Daniel Bedingfield, Ed Sheeran, Calvin Harris, Sam Mangubat, Stormzy, Sofie Hagen, Gemma Collins, Matt Kilgallon, Shona McGarty, Alexandra Burke, Michael Devlin, Scott McKenna, Dominic Ball, Dan Osborne, Union J, James Arthur, Zhong Chenle and Robert Pattinson have recognized their love for Westlife's music. Some well-known music artists like Ronan Keating,  Will Young, Shayne Ward  and Ruben Studdard have also covered their songs. Some of the following are original songs by Westlife that have been covered by other artists (which includes professionally recorded or performed list only). Some were officially released as a single. 

Despite their popularity, some artist have expressed their dislike to the group like Eminem, Christina Aguilera, Bob Geldof, Pierce Brosnan, Liam Gallagher, Melanie C, Victoria Beckham, Gary Barlow, Damon Albarn and Noel Gallagher. Some have also criticized the band for having lots of covers, having the same sound on every albums released and lack of songwriting skills. Feehily revealed in 2009: "There were many songs which I would be even scared to mention, you know, that were suggested to us which we turned down. "There were many cover versions and many original songs that were either terrible. There was loads of stuff through the years, like 'You Are Not Alone' by Michael Jackson?, that were suggested by their record company chief Cowell". Westlife have proven to have more original songs, worked with many songwriters and music producers and co-written numerous songs throughout their 14-year career.