Ardstone Capital has agreed terms to buy three office blocks totalling 85,000 sq ft from Standard Life for around £20m.
The King Street offices were put on the market in October 2014 with an £18.25m price tag.
The grade 2-listed 11-storey building, refurbished in 2002, contains 85,460 sq ft of commercial office space across three buildings.
Current tenants include law firm Weightmans and commercial property consultant Rapleys.
A spokesman for Ardstone confirmed that it had put the building under offer but declined to comment on the purchase price.
JLL is advising Royal London on the sale of Pall Mall.