The newly refurbished 80,000 sq ft business park, near Warrington, is 56% let following completion of the revamp this month.
St James is home to more than 30 businesses, ranging from smaller enterprises to larger listed PLCs.
Tenants include motor market experts Auto Trader, in 9,470 sq ft, chip and pin technology specialists ICC, 2,525 sq ft, telecoms specialists WHP Projects, 4,097 sq ft, the Royal British Legion, 3,387 sq ft, and the Labour Party, 1,590 sq ft.
John Downes, chief executive of Langtree, said: "We believe this regeneration offers businesses top-class facilities in a great location, and that's why we're seeing new firms and fresh investment coming in.
"Despite the wider economic conditions, each of our existing business centres nationwide is well occupied. We pride ourselves on the quality of environment and finish that we offer. Successful businesses want to be associated with the highest standards."
St James Business Centre offers free on-site parking, a cafe, meeting rooms for hire, conferencing facilities and secretarial support to the serviced offices, as well as a children's nursery.
Five new companies have taken offices within the past month, including the Atlantic Gateway Partnership.
The agents for St James Business Centre are the Warrington-based Eileen Bilton Partnership.