The bank said that "due to changes in commercial priorities" it would not sponsor the event beyond 2016.
It has sponsored the event, which features the top eight men's players in singles and doubles, since 2009 when it moved to London's 02 Arena.
Barclays has also dropped sponsorship of the Premier League and London's "Boris bikes".
A spokesman said the bank was going through a period of change and it was re-assessing the way its portfolio of sponsorships worked for the company.
The bank has not disclosed the value of the tennis deal.
Separately the Daily Mail reported that the World Tour Finals would remain at the 02 Arena until at least 2018. There had been speculation that it would move elsewhere - with interest from North America and Abu Dhabi.
This year's event takes place from 15-22 November.

The 30-year-old from Ashford, Kent, admitted the offences against victims aged between six months and 12 years, from 2006 to 2014.
He was given 22 life sentences and will serve a minimum term of 23 years.
It is believed Huckle abused up to 200 children from mainly poor communities in the Malaysian capital, Kuala Lumpur.
He presented himself as a practising Christian and first visited Malaysia on a teaching gap year when he was 18 or 19. He then went on to groom children while doing voluntary work.
Sentencing Huckle, Judge Peter Rook QC said: "It is very rare indeed that a judge has to sentence sexual offending by one person on such a scale as this."
He added that Huckle's life "revolved around your obsession with your own sexual gratification by child sex abuse".
How abuser Richard Huckle was caught
Malaysian reaction to Huckle's abuse
"It is also clear that, had you not been arrested, you planned to continue the same lifestyle using the expertise that you were keen to show off to and share with other abusers so as to continue your sexual exploitation of the children of such communities."
Investigators found more than 20,000 indecent pictures and videos of his assaults on children, which were shared with paedophiles worldwide through a website hidden in the so-called dark web
He even tried to make a business out of his abuse by crowd-funding the release of the images and was compiling a paedophile's manual at the time of his arrest by the National Crime Agency in December 2014.
He boasted about his crimes in online posts, saying in one discussion that "impoverished kids are definitely much easier to seduce than middle-class Western kids."
Ahead of his sentencing, Huckle claimed to a psychiatrist that he wanted to put his "madness" behind him and settle down with a south Indian woman.
But the court was shown a posting from 2013 in which he outlined his plan to marry one of his victims in order to help him abuse more children.
Judge Rook said: "In my view, you may well harbour feelings of regret but there is no feeling of genuine remorse in this case."
James Traynor from the NCA's child exploitation and online protection command said Huckle had "deliberately travelled to a part of the world where he thought he could abuse vulnerable children without being caught".
"He spent several years integrating himself into the community in which he lived, making himself a trusted figure. But he abused that trust in the worst possible way.
The NCA were able to use legislation which allows UK nationals to be prosecuted in the UK for offences that have been committed overseas.
Mr Traynor added: "Borders are no barrier - we are determined that those who go abroad to abuse children will be held to account."
The NCA has now referred itself to the police watchdog over the way it handled parts of its inquiry.
Huckle is known to have returned to the UK and attended two churches in Kent and London.
But the BBC has learned that the NCA only contacted the churches - which cannot be identified for legal reasons - last week, almost 18 months after Huckle was first arrested.
It says it has now referred that aspect of its investigation to the Independent Police Complaints Commission to see if it could have improved its response.
Barclays Bank is to end its sponsorship of the ATP World Tour Finals tennis tournament.
[NEXT_CONCEPT]
British man Richard Huckle has been jailed for life by a judge at the Old Bailey after admitting 71 charges of sex abuse against children in Malaysia.