Lewis Brisbois Bisgaard & Smith is staying put.

The law firm, forced from its longtime home at 221 N. Figueroa St. in December when flames spread from an arson fire at the adjacent Da Vinci apartment complex, had taken temporary space at the U.S. Bank Tower in a year-end deal that was the largest lease signed in 2014.

The firm is now closing in on a deal to stay at the downtown L.A. building at 633 W. Fifth St. and is on the verge of signing a 15-year, 215,000-square-foot lease valued at as much as $115 million, according to a source with knowledge of the deal. The deal would commence in January, after Lewis Brisbois’ short-term lease ends.

With 277 attorneys in its local offices, Lewis Brisbois is the largest law firm in Los Angeles. The city owns the firm’s previous home and after the fire agreed to allow Lewis Brisbois to return to the building, find another location or extend its lease at U.S. Bank Tower. Both the law firm and the city had the option of terminating the lease at 221 N. Figueroa.

Overseas Union Enterprise, the Singapore-based owner of U.S. Bank Tower, will install prominent Lewis Brisbois signage on Fifth, Hope Street and in the building’s lobby under the terms being discussed, the source said. Also part of the deal is an opportunity to expand as well as modify the space.

Lewis Brisbois is being represented by Jonathan Larsen, a principal at Avison Young who represented the firm in its move to U.S. Bank Tower last year. The building is being represented by OUE’s leasing director, Peter Johnston, and John Eichler at Cushman & Wakefield.

Neither Tim Graves, the law firm’s L.A. managing partner, nor the brokers would comment on the pending transaction.

The 1,432,539-square-foot, 72-story Class A office building is, for now, the tallest building west of the Mississippi. (The Korean Air Tower under construction downtown will take that mantle when completed.) It is 82.6 percent occupied by tenants that include U.S. Bank, which takes 105,000 square feet and is the second-largest tenant, and a number of other law firms.