They were written off as a novelty act when they first came to fame as winners of television reality show The Sing-Off in 2011.

Since then, American a cappella act Pentatonix has become a force to be reckoned with in the global pop world.

Albums such as their 2015 self-titled release and 2016's A Pentatonix Christmas topped the Billboard charts, their list of awards include three Grammys and their YouTube videos have clocked more than 4.4 billion views.

Speaking in a telephone interview from Los Angeles ahead of their concert at The Star Theatre on Feb 11, co-founder Scott Hoying says the last decade has been a dream come true.

"As a musician, you dream of getting to play Madison Square Garden, winning a Grammy, getting to tour the world with friends, that's the big goal, that's my vision. In the 2010s, I got to do all of that, I checked off everything on my bucket list," says the 28-year-old.

Pentatonix, formed in Texas in 2011, also comprise singers Mitch Grassi, Kirstin Maldonado, Kevin Olusola and Matt Sallee.

Here are five ways the quintet worked their way up to be one of the most successful vocal groups in the music industry today.

1 They are savvy on social media

They have built up quite a fan base through social media - 17.7 million subscribers on YouTube, two million followers on Instagram, 3.6 million on Facebook - but Pentatonix leave nothing to chance.

Hoying attributes their success to their constant engagement with fans online.

"A huge reason is just us being able to connect with fans direct via YouTube and social media. We keep putting out content. And we enjoy it and I think whenever someone's authentically enjoying something, you can feel that. I think that energy has propelled us for so many years."

2 They have never lost at the Grammys

Pentatonix have won every time they have been nominated at the Grammys.

BOOK IT /PENTATONIX - THE WORLD TOUR SINGAPORE 2020

WHERE: The Star Theatre, 04-01, 1 Vista Exchange Green WHEN: Feb 11, 8pm ADMISSION: From $88 from Sistic (go to www.sistic.com.sg or call 6348-5555)

As a musician, you dream of getting to play Madison Square Garden, winning a Grammy, getting to tour the world with friends... In the 2010s, I got to do all of that. PENTATONIX'S SCOTT HOYING

In 2014, they won Best Arrangement, Instrumental Or A Cappella for Daft Punk, their vocal medley of songs by the iconic French electronic act. They won in the same category the following year for their take on Tchaikovsky's Dance Of The Sugar Plum Fairy.

They won their most recent Grammy in 2016 for Best Country Duo/Group Performance with Jolene, a duet with country music legend Dolly Parton.

3 Christmas hits are songs with a long shelf life

Scoring holiday hits is one way to ensure your songs get played every year. Pentatonix have plenty - PTXmas (2012), That's Christmas To Me (2014), A Pentatonix Christmas (2016), Christmas Is Here! (2018) and The Best Of Pentatonix Christmas (2019) - and they have all charted in the top 10 in the United States pop charts.

4 They perform regularly for fans all over the world

Since 2012, Pentatonix have toured tirelessly around the world, playing regular shows in North America, Latin America, Europe and Asia.

Their Star Theatre show will be their fourth in Singapore, after performances in 2014, 2015 and 2016.

Hoying says of their upcoming concert: "We're going to do a lot of originals, we'll do a lot of covers the fans have never seen live and there will be a lot of interaction with the audience, singalong stuff.

"It's a really fun show. I think it's the strongest tour we've ever put together."

5 They do not just rely on covers

Their best-known tunes are the a cappella covers of both contemporary (Daft Punk) and classic (Hallelujah) hits, but they also have their fair share of original songs such as Can't Sleep Love (2015).

Hoying says the group is working on new originals and plans to release them this year.

"I really enjoyed writing them because I feel like everyone in Pentatonix has experienced so much more now. And so our new original album, it's definitely going to be even more honest songwriting and I feel like it's more mature songwriting."