The deal with bank Bradford & Bingley would eclipse that between Hampshire and Powells Group, worth an estimated £300,000 over two years.
The deal sees Bradford & Bingley installed as Yorkshire's official club sponsor, with the bank's branding to appear on all player shirts, sweaters and training kit, along with mascot attire and replica shirts, reports the Yorkshire Post.
Branding will also appear throughout the Headingley ground and on the club's official literature and website.
The deal will help the club push through its ground redevelopment plans, after it recently acquired the freehold to the venue.
