It was number one within 10 hours of being released, overtaking last week's official UK number one Gangnam Style.
The full single was released at 00:07 BST, after a 90 second clip was apparently leaked online this week.
The 23rd Bond film, Skyfall - Daniel Craig's third outing as 007 - is released in UK cinemas on 26 October.
Adele ended months of speculation over her involvement on Monday, when she posted a picture on Twitter, featuring the cover page of the sheet music for the Skyfall theme, bearing her name alongside that of longtime producer and co-writer Paul Epworth.
Epworth told BBC 6 Music that the "dark and moody" theme was intended to echo the narrative of the film.
"The [Bond theme] songs seem to fall into groups, in terms of subject matter," said Epworth. "Some of them have a romanticism to them, and some of them are very much about the narrative of the film.
"We went very much with the narrative of the film. We talk a lot about Bond's relationship to the country... and to MI6.
"There's a little bit of that in the lyrics, and I guess we were trying to find a way to almost make that romantic, you know?
"I think you will need to see the film and see where the song happens in the context of the film.... and it will all make sense."
Skyfall was recorded at Abbey Road Studios in London, and features a 77-piece orchestra.
Adele broke her silence on the track in an official message on the James Bond website on Monday: "When we recorded the strings, it was one of the proudest moments of my life.
"I'll be back-combing my hair when I'm 60, telling people I was a Bond girl back in the day, I'm sure!"
The singer admitted she was a "little hesitant" about accepting the challenge because of the "instant spotlight and pressure" that came with a Bond song.
But, she said it ended up being a "no-brainer" after she fell in love with the script.
Although it is an entirely original composition, Epworth said they worked hard to give it, "the James Bond feeling", and it was "definitely a conscious thing" to reference Monty Norman's famous four-note motif from the James Bond Theme after the first chorus.
And Monty Norman has given Skyfall his seal of approval, telling the BBC: "I think it's very good, it works for the film very well and I'm honoured that it gives a large nod towards my original."
Norman continued: "In a sense it's a pretty sensible thing to do, if you want to feel the 'James Bond quality' of the music.
"Whatever one thinks of the James Bond Theme, and most people seem to like it, that is the signature tune of the James Bond films so if you use that kind of quality as they've done, that's good."
Norman, who wrote the theme for the first Bond movie, Dr No, 50 years ago, said he thought the Bond franchise had made the right choice in Adele.
"I think Adele's terrific, a truly good singer - one of the best singer's that we've had for many years. She can only go from strength to strength," said Norman.Chart history
While Skyfall had topped the UK's iTunes chart within hours of its release, it has some strong competition in the official singles chart this weekend.
It has been a big week for new singles according to Martin Talbot, managing director of the Official Charts Company.
He said several tracks are looking to unseat last week's number one, global YouTube phenomenom Gangnam Style.
"Although it will only have two days' sales to contribute towards its official singles chart position this Sunday, Skyfall is likely to be chasing the tails of Rihanna's Diamonds and One Direction's Live While We're Young, both of them brand new singles," explained Talbot.
"Given her massive popularity, we wouldn't put it past Adele to add to her many chart records by registering the very first James Bond Official Number One Single, whether this Sunday or in future weeks," he added.
Duran Duran's A View To A Kill is still the highest-charting Bond theme. It went to number two in the UK Charts in 1985, and topped the Billboard Hot 100 in the US.
The band's John Taylor gave the BBC his verdict on Adele's Skyfall.
He wrote: "Pure Bond DNA, an instant classic. Delivers everything I want to hear from a Bond theme."