Celebrating its centennial this year, Cushman & Wakefield Inc.’s big splash in Los Angeles came 50 years ago, when John C. Cushman III was tapped to lead the largest leasing challenge the city had ever seen – filling Arco Plaza, now called City National Plaza, a 52-story, 2.6-million-square-foot twin structure downtown.

One study suggested it would take 15 years to lease the building; Cushman said he did it in about three.

“The project was a home run,” said Cushman, chairman of global transactions.

Cushman & Wakefield grew to become the second-largest commercial real estate brokerage in Los Angeles County, handling deals worth $10.2 billion in 2015, including 4,500 leases and 5,700 sales. It was L.A.’s third-largest property management company as of the end of last year, with a local portfolio of 22.8 million square feet.

“Cushman & Wakefield has touched the development of most of the major buildings in downtown Los Angeles,” Cushman said.

But it all started on the other side of the country, when J. Clydesdale Cushman and Bernard Wakefield, Cushman’s grandfather and great uncle, co-founded the Cushman & Wakefield property management firm in New York in 1917.

In 1929, the firm opened a rental office in the General Motors building and soon became a leader in real estate services in the Big Apple. One significant deal early in its history was the sale of the land for what would become the United Nations building.

In 1963, John Cushman began to work for the firm, opening its first L.A. office in 1967 while handling the Arco Plaza deal during a period of national expansion. Cushman & Wakefield also brokered a deal in the late 1960s that led to the building of the Sears Tower in Chicago.

RCA Corp. acquired Cushman & Wakefield in 1969, then sold its stake seven years later to the Rockefeller Group. Cushman left the firm in 1978 and opened a firm called Cushman Realty Corp. with his twin brother, Louis B. Cushman.

By the 1990s, Cushman & Wakefield was expanding its operations further, establishing partnerships with major real estate firms in the Americas, Europe, and Asia.

The 2000s were a period of acquisitions for the real estate service firm, including buying Cushman Realty in 2001, with the brothers rejoining the firm.

Italian investment group Ifil, now known as Exor, purchased a 71.5 percent stake in Cushman & Wakefield in a $625 million cash deal in 2007. In 2015, Cushman & Wakefield merged with Chicago commercial real estate firm DTZ in a $2 billion deal, keeping the former’s name and creating one of the largest real estate service firms in the world, with annual revenue of $5 billion and more than 43,000 employees.

Cushman & Wakefield has recently received more attention in Los Angeles for handling a project similar in prominence to Arco Plaza: leasing the Wilshire Grand Center, now the city’s tallest building. Cushman said he expects to have the property’s 353,000 square feet of office space fully leased by the end of the year.

The spire dominating the L.A. skyline is a potent symbol of the city’s continuing importance for Cushman & Wakefield.

Andrew McDonald, the firm’s regional managing principal and executive managing director in Los Angeles, said the booming L.A. economy, continues to make the city a key piece of the firm’s portfolio.

“Los Angeles might be the most unique (market) in that … it is the content capital of the world,” McDonald said. “And it’s also among the most important technology geographies of the United States.”

Cushman & Wakefield is set to relocate its Torrance office on May 5 to a larger 12,000-square-foot site in El Segundo, one of the firm’s eight locations in L.A. and Orange counties.

“El Segundo offered us a more strategic location to be close to clients that are growing at a breakneck pace at the southern part of the bay.” McDonald said.

Staff reporter Kat Speed contributed to this report.