Lee was a member of pop group Blue although most recently appeared in the cast of EastEnders.
He'll be the second Blue star to take part after bandmate Simon Webbe competed in the 2014 series.
Lee joins Pussycat Dolls performer Ashley Roberts and Steps singer Faye Tozer who are also both said to have agreed deals to compete for the glitterball in 2018.
A source told the Daily Mirror newspaper: "Lee will make great TV - he’s naturally charismatic and very funny. He is totally unfazed by the curse."
Alongside the pop singers, YouTuber Joe Sugg will join the Strictly Come Dancing 2018 cast, it's been reported.
The vlogger, brother of fellow online celeb Zoella, will be the first YouTuber to appear on the BBC One series.
A source said: "Joe has done extremely well for himself on YouTube and after a lot of negotiation he’s agreed to give Strictly a go. He thinks this will be a good launch pad to go."
They added to the Metro newspaper: "Zoe, Alfie and the rest of his YouTube friends are going to be there supporting him in the audience every week – even if he’s not the best dancer his fanbase is a force to be reckoned with."
Joe joins a growing list of celebs rumoured for Strictly 2018.
Also said to have signed up for the cast this week are BBC News journalist Kate Silverton, This Morning’s Dr Ranj, Capital FM radio DJ and TV presenter Vick Hope on this year's line up.
A spokesperson for the BBC commented on the reports: “We don’t comment on speculation and the full line-up is coming soon.”
For now, other rumoured names Strictly Come Dancing bosses could sign this year include TV personality Anneka Rice, football pundit Chris Kamara and Radio DJ Maya Jama.
Hollyoaks star turned Oscar winner Rachel Shenton and The Chase's Mark Labbett have also been tipped to take part in Strictly Come Dancing 2018, alongside former England footballer David James and X Factor star turned TV host Rylan Clark-Neal.
Strictly Come Dancing begins on BBC One in September with its pre-recorded launch show.