The 'Flying Without Wings' hitmakers - which are comprised of Mark Feehily, Shane Filan, Kian Egan and Nicky Byrne - have enjoyed huge success with their 'Twenty' reunion tour so are planning a huge concert series across the globe next year, as well as a TV special and more new music.
However, the plans won't kickstart until after Mark and his fiance Cailean O'Neill have welcomed their baby daughter into the world.
A source told Mirror Online: "Westlife's comeback tour has been a remarkable success and interest in their new music has been better than the band ever imagined, so plans are well underway for what comes after the album release in November.
"The boys are in big demand. Mark is going to take a short break when his new baby arrives but then it's all systems go.
"TV execs want the boys for the Christmas schedules and there is already talk of a big world tour in 2020, plans are being drawn up.
"There will also be even more new music with Ed Sheeran . Westlife are popular again. The 'Twenty Tour' sold 700,000 tickets. There is a lot more to come from them, they're in it for the long-term now."
Mark, 39, is likely to bring his baby on the road with him as he praised the family-orientated backstage atmosphere on the 'Twenty Tour', admitting it has been very different to the group's "older days".
He said: "It just feels like the right time to start a family now. It is something that I've always wanted to do but it has always been about timing.
"Cailean and I are really happy and now that I'm in my late 30s and settled at home in Sligo, it is the right moment.
"The Westlife lads have all got nine kids between them, ours will be the tenth Westlife baby. What's been great about this recent tour is that all of the families have been involved, kids and all, running around backstage
"It is different from the older days but it is just brilliant. Having everyone around us brings a fantastic energy. We've had to set up a special family room for everyone at every stadium and arena we've played at, it's been great. The Westlife kids have loved it I think."