Downtown L.A.’s PacMutual, which has been repositioned to appeal to creative office tenants, last month signed its second-largest lease with an unexpected tenant: a new law firm.

Trial lawyers John Hueston and Brian Hennigan formed Hueston Hennigan in January after splitting from Century City firm Irell & Manella, taking four other Irell partners and more than 20 associates with them. The new firm signed a lease late last month for 21,000 square feet in the 446,023-square-foot Class A office complex at 523 W. Sixth St. The property is now 95 percent leased.

“This demonstrates that well-executed creative office space is the new Class A in downtown Los Angeles, and Hueston’s lease is further evidence of its broad appeal,” said Carle Pierose, a partner at Santa Monica’s Industry Partners, who represented landlord Rising Realty Partners in the transaction.

Terms of the deal were not disclosed, but industry sources said it was a five- to seven-year lease valued at about $9 million.

The firm has occupied 6,000 square feet of temporary office space in the building since January, and about 30 people will work in the space when construction is complete.

Rising bought the building for $60 million in 2012 and has spent about $25 million to upgrade and reposition it as a creative office complex.

Asking rents at PacMutual, near Pershing Square in the Central Business District, are as high $4 a square foot, according to CoStar Group Inc., surpassing the $3.29 fourth-quarter market average for downtown, according to data from Jones Lang LaSalle Inc. There have been 58 lease deals signed in the building over the last two years.

Hueston Hennigan, a white-collar criminal defense practice, chose the location because it was close to the courthouses. The office is being built out to include lawyer offices around the perimeter and group stations at the center.

“We want to emphasize people coming together to share ideas,” said Moez Kaba, a founding partner. “It’s not a hierarchical space with the senior partners locked in their offices, so it is going to be more like what you’d imagine for a Silicon Beach startup space.”

Mike McKeever, a senior vice president at the downtown office of Jones Lang LaSalle, represented Hueston Hennigan in the deal. He said creative office space is in short supply downtown, especially in the Central Business District.