The Cambridge University Library has housed the Codex Zacynthius since 1984.
It was offered first refusal to buy the New Testament manuscript and had until the end of August to find the funds.
The fate of the historical text had been in doubt after the Bible Society in Swindon, which owned it for almost 200 years, decided to sell it off to raise money.
The society, which was presented with the 176-page volume in 1821, wanted to shore up funds for a new £1m visitor centre inside a deconsecrated church in North Wales.
Dr Rowan Williams, the former archbishop of Canterbury who supported the Cambridge University Library's fundraising campaign, said securing the text would allow further study.
The bible features an early seventh century script which has been partially scraped away and written over to make way for a 13th century entry.
It is regarded as an important text in studying the development of the New Testament.
"The discovery and identification of the under-text represents a fascinating detective story," Dr Williams said.
"By securing the manuscript, we hope that multispectral imaging techniques will enable scholars to recover fully the hidden text."

The call handling and IT system is more than Â£40m over budget and was initially due to be ready for October 2013.
An earlier attempt to introduce the system had to be abandoned.
The programme will now be phased in for some services from this summer with a national roll-out by the end of 2017.
Earlier this year, the planned June launch was pushed back to the "summer of 2016" after an issue that caused computer screens to appear blank.
It followed an earlier incident in which the system crashed and staff had to resort to pen and paper to deal with patient calls.
The new technology is meant to make NHS 24 more efficient but is expected to cost Â£117m, more than 50% higher than the original estimate.
NHS 24 said the new telephone system would be in place this year for services including Breathing Space, NHS Living Life, the musculoskeletal helpline, death certification, blood transfusion and Fit For Work.
It will then be introduced in one health board area to ensure it is working effectively before the national roll-out.
NHS 24 chief executive Angiolina Foster said: "We expect to have a functioning technology system tested and available later in the summer.
"However, we have recognised that ensuring our staff and operational environment are also fully ready to accept the technology is absolutely essential to making sure we can make a smooth transition to the new system."
Ms Foster said: "We recognise that the past 18 months have been challenging for the organisation and know that the professionalism and dedication of our people has enabled us to give high-quality care to patients during this time."
Health Secretary Shona Robison said: "While any delays to implementation are disappointing, patient safety must always come first. This is why NHS 24 has taken the decision to phase the roll-out of its Future Programme.
"This decision follows a comprehensive review of the new system which concluded that a phased roll-out later this summer, working towards full implementation across all health boards by the end of 2017, would be both safe for patients and deliverable by the organisation."

Mr Byrne was shot dead in the Regency Hotel during a boxing weigh-in in the north of the city in February.
This is the second search to be carried out in a week.
RTÉ has reported that searches are being carried out on ten houses and flats in Dublin's south inner city.
The operation began at around 06:30 local time on Friday morning.
It is understood that over 80 armed gardaí are involved in the investigation, as well as the Emergency Response Unit, the Drugs and Organised Crime unit and the Criminal Asset Bureau.
On Wednesday, Irish authorities seized over 1m euros (£770,000) worth of luxury cars, cash and other valuables.
Scholars have hit their target of raising £1.1m to secure the future of an early Biblical manuscript.
[NEXT_CONCEPT]
A crisis-hit computer project for the NHS 24 telephone helpline will not be fully rolled out across Scotland until the end of next year - four years later than originally planned.
[NEXT_CONCEPT]
Irish police have begun another series of raids on properties linked to members of a criminal gang connected to shooting victim David Byrne in Dublin.