The seven-track compilation features collaborations with the Military Wives, Hayley Westenra, Alfie Boe and Laura Wright. It also contains his cover of 'Here Comes the Sun', which was recently featured on a Marks and Spencer advert.
The album gives Barlow his first number one LP without Take That since 1997's Open Road.
Barlow said of the honour: "I couldn't have wished for anything more on this momentous weekend!"
'Sing' co-writer Lord Andrew Lloyd Webber added: "I'm absolutely thrilled, this is a burst of sunshine on a rainy Sunday - let's hope the sun shines on Gary's concert tomorrow."
The top five is dominated with new entries, with Paloma Faith entering at number two with Fall To Grace, having led the pack all week.
Rumer lands at three with new album Boys Don't Cry, with the Scissor Sisters securing a fourth top five album with Magic Hour at four. Russell Watson's compilation Anthems enters at five.
Emeli Sandé falls to six with last week's number one Our Version of Events, while Adele almost finally leaves the Top 10 by falling seven to ten with 21.
Coldplay's new tour sees Mylo Xyloto climb up 11 spots to 11, while John Mayer drops 26 places to 30 with Born and Raised. Last week's runner-up Joe Bonamassa falls 31 places to 33.
Sigur Rós's sixth studio album Valtari is a new entry at eight, while Melody Gardot's The Absence enters at 18. Alt-J's An Awesome Wave lands at 19.
Ultravox's first album with their best-known lineup since 1986 Brilliant enters at 21, with Regina Spektor scoring a number 24 entry with What We Saw From the Cheap Seats.
Public Image Ltd's first studio album for 20 years This is PiL is a new entry at 35.
Watch the video for Gary Barlow's 'Sing' below:
Source: Official Charts Company
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