In a statement posted on the London Stock Exchange this morning, the bank confirmed the activist's move: 'Barclays notes that Sherborne controlled entities have acquired voting rights over 5.16% of its issued share capital.
'As with all its shareholders, Barclays will continue to engage with Sherborne, and welcomes them as a shareholder.'
The Sherborne stake is a combination of derivatives and shares, worth £580 million.
'Sherborne Investors has advised the company that its turnaround assumptions indicate a potential return on the investment in line with Sherborne Investors' customary return objectives,' a statement from the vehicle read.
The purchase comes after US hedge fund Tiger Global bought a 2.5% stake in Barclays at the start of the year.
At 9.45am shares in Barclays had jumped 4% to 217.95p as the market welcomed Sherborne's move.
AJ Bell investment director Russ Mould was not surprised by the positive response in Barclays' shares, especially given how cheap they look. He believes the prospects of 'shake-up' at Barclays have risen now Sherborne has appeared on the shareholder register.
'Sherborne has built a formidable reputation for squeezing improved financial and operational performance from the companies in which it invests and Edward Bramson clearly feels that Barclays shares are going cheap, given the prevailing discount to the book, or net asset value,' Mould said.
'The question now is what the activist investor thinks Barclays should be doing differently and how he intends to get those views across to the bank’s boss, Jes Staley.'
According to the Financial Times, Bramson (pictured) has met with the Barclays board to discuss its full-year numbers.
Barclays released its results in February, showing a 10% increase in 2017 core profit to £3.5 billion.
However, this failed to drag Barclays back into the black with exceptional costs on the sale of its Africa division and tax changes causing a £1.9 billion loss.
Pretax profit was up from £3.2 billion in the prior year but remained well short of the £4.7 billion analysts had forecast. On a post-tax basis the business last year reported a £1.6 billion profit.
The bank has also promised to reinstate the dividend it cancelled two years ago.
In a statement accompanying the results, chief executive Jes Staley said: ‘2017 was a year of considerable progress for Barclays.
'While we still have a number of legacy conduct issues to address, I am confident in the capacity of this business to generate excess capital going forward, and it remains our intention over time to return a greater proportion of that excess capital to shareholders through dividends and other means of capital distribution, including buybacks.'