The bank reported that online and telephone operations went down at 10am.
By 5.30 pm, Barclays’ website claimed online and mobile banking was back to normal.
It said telephone services had also been restored but were suffering delays because of high call volumes.
Some customers tweeted their frustration throughout the day.
One customer, Chris Williams, posted to say he had been trying to log in for over an hour; another asked: “when can I use the online bank again – and is my money safe?”
The problem comes just months after a prolonged period of IT troubles left TSB customers locked out of their bank accounts.
The bank said: “We’re sorry about today’s problems with online banking, telephone banking and some features in Barclays mobile banking.
“We’re happy to say that everything is now fixed – thanks for bearing with us.”
The bank had also acknowledged earlier in the day that services in their branches were intermittent.
A number of business customers had complained that they were unable to organise tomorrow’s payments for staff while other users, after the bank had given the all clear, suggested they were still having problems completing their banking tasks.