James Fisher Nuclear has taken a lease on the 30,000 sq ft Gordon House in Bamber Bridge.
Five-year terms were agreed with landlord AMEY at a rent of around £15/sq ft.
James Fisher Nuclear is expected to relocate from its existing premises in Leyland as part of expansion plans.
The three-storey building in Spectre Way was originally purpose built for The Woodford Group in 1999 and has been vacant for some time.
Cushman & Wakefield are the sole letting agents on the property.
Jonathan Baucher, partner of Cushman & Wakefield, said: "This was a significant letting for the region and represents one of the largest office lettings to be completed in the local market over the last decade. We are continuing to experience strong levels of occupational demand across the region and this latest transaction is evidence of this trend."
James Fisher Nuclear were unrepresented.