The woman had been protesting against the bank's alleged investment in fossil fuels when the branch was targeted at 1.20pm on Saturday (August 15).
Pink paint was splashed across its windows as the woman shared her grievances with shoppers walking past on the high street.
She has been arrested on suspicion of criminal damage.
A spokesman for Lancashire Police said: "We were called to reports of criminal damage at a commercial premises in Fishergate, Preston, at 1.20pm on August 15.
"A 62-year-old woman from Preston was arrested on suspicion of criminal damage. She has since been released on bail.
"No charge has been made – she has been bailed until September 6."
Footage of the incident has been shared widely online.
In response to the protest, a Barclays spokesperson said: “We want to take a leading role in tackling climate change as we recognise that it is one of the greatest challenges facing the world today.
"Our ambition is to become a net zero bank by 2050, and we’ve made a firm commitment to align our entire financing portfolio to the goals of the Paris Agreement.
"That means our own operations, and the financing we do for our clients, in every sector, will support the transition towards a low-carbon economy."
Barclays said it is helping police with their investigation.