The majority of the jobs, 43, are posts that are being transferred from the firm's offices in the US and Europe.
The remaining 24 positions are to be created as a result of "projected natural growth at its Belfast office over the next three years".
Invest NI has offered the firm Â£348,400 to support the move.
The money is in addition to the Â£2.5m that Invest NI gave them two years ago, to support the firm's decision to relocate to Northern Ireland.
It is understood that the 43 employees whose jobs are due to be transferred to Belfast will be offered the option of relocating to the city.
Should they decline, their posts will then be advertised.
Enterprise Minister Arlene Foster welcomed the announcement as "positive news for our economy and the legal services sector".
"Having located here in 2011, Allen & Overy has rapidly grown its presence and is already well ahead of its recruitment schedule with 300 people employed across a range of support and legal functions," the minister added.
In February 2011 the firm announced it was moving 180 back-office jobs from its base in London to its new office in Belfast, and said it believed it could save Â£10m over five years through its relocation to Northern Ireland.
At the time, the firm also said it hoped to employ as many as 300 staff based in Belfast by 2014.  The jobs announced on Thursday are in addition to that 2011 figure.
Andrew Brammer, Head of Allen & Overy's Support Services Centre, said: "Since our investment in 2011 we have been continually impressed with the contribution our Belfast office has made in supporting the delivery of high quality legal services to Allen & Overy's international client base.
"We are ahead of where we thought we would be in terms of recruitment under the original investment as we have found a wealth of highly skilled and talented people from which to grow our operation.
"In a difficult global economy, Northern Ireland has provided us with an effective and competitive location from which to grow our business," he added.
The international law firm, Allen and Overy, has announced it is bringing 67 jobs to its legal services centre in Belfast.