There is such a thing as a merger of equals, and it exists in Los Angeles.

In a town where marriages last about as long as a Snapchat, Interpublic's odd coupling of high-wattage talent-publicity firm PMK/HBH with brand-PR agency BNC in 2010 seemed destined to end in irreconcilable differences. The merged PMK-BNC had a tongue-twisting name, vastly different client portfolios and three CEOs with contrasting backgrounds.

"When we met [after the merger], they took out their pads," recalled powerhouse publicist and Chairman-CEO Cindi Berger, referring to co-CEO and Chairman Michael Nyman and co-CEO Chris Robichaud. "They had matching graph-paper pads! I called them my Graph-Paper Boys and said, 'You're both so corporate.'"

Since that day, the graphs on that paper have gone straight up. PMK-BNC has posted double-digit growth each year and, according to Ad Age DataCenter estimates, the shop's revenue in 2013 climbed 18% to $50 million.

Now that it's shown that the pairing can work, the firm is fine-tuning its strategy. PMK-BNC wants to get its brand-celebrity pairings down to a science -- literally. Using its "Fanatomy" tool (see example at end of story), the shop cross-checks various data points to create a pairing based on consumer draw. It also recently launched a practice that advises celebrities on expanding their personal brands. And in April, the shop acquired digital agency Spokes and launched a separate digital group called Vowel.

Two sides of PMK
The secret to its success is its seeming mismatch. In a world where brands and talent are partnering and access is everything, PMK-BNC brings together under one roof A-list star power and brands seeking talent for content collaboration. That booming business has boosted the shop's top and bottom lines; it's now sprawled to more than 250 staffers in L.A., New York and London.

In her New York office, Ms. Berger paces while talking on a headset, à la Jerry Maguire, to a publicist about an event featuring a celebrity client. Her roost is decorated with framed clippings and a photo of her with Robert Redford taken in the rugged outdoors. On a large, comfy chair sits a small white pillow with silver lips on it, a gift from another longtime client, Barbara Walters. Among the other A-listers keeping the shop busy: Miley Cyrus.

Ms. Berger's main office is in New York, but across the country is the company's Pacific Design Center Headquarters, housing both the brand and entertainment divisions. This looks like every other corporate office in need of a facelift, with cookie-cutter office space. But it's in tune with the agency's other half, representing corporations like Samsung and Diageo. Here, brand CEO Chris Robichaud holds sway over an operation that, among other things, generated buzz for Audi's Emmy sponsorship a little over two years ago with a video called "Emmy Training Day."

PMK-BNC masterminded the video, in which 2010 Emmy announcer and client Joel McHale put 2011 announcer Melissa McCarthy through a hard-core training session, complete with boxing matches and a chicken chase. And last year, the agency created a buzzy "Star Trek Into Darkness"-themed video for Audi that featured non-clients Leonard Nimoy and Zachary Quinto, who've both played Spock in the franchise.

"I was on a press junket and the [celebrity] talent was bringing it up on their own," said Andrew Lipman, general manager-communications for Audi. "For a PR person, the dream is when these things spread organically."

Mr. Nyman oversees both sides of a business that's become one-stop shopping for people like Mr. McHale. "I know [PMK-BNC] will come in handy when I start asking for favors and we start making pilots and try to get talent," said "The Soup" host during a takeout lunch from Nobu. "I can walk across the office [to the talent-agent wing] and be like, 'Hey, dork, I want your client on my show.'"

Even balance
When PMK-BNC's leaders came together in 2010, the business was 60% skewed toward entertainment PR, which encompasses talent, music and film. It's since become more evenly balanced.

"Our brand business has doubled over the last couple years and expanded from brands that just wanted PR," said Mr. Robichaud. "We're adding digital marketing, content and production."

As film studios put less muscle behind marketing and look to advertisers to help foot the bill, PMK-BNC's brand clients are also benefiting from the changing entertainment world.

"The rules have loosened," said Mr. Robichaud. "[A brand] can do a placement around a film and not be in a film," such as Audi ambushing the "Star Trek Into Darkness" buzz with its video, doing an end run around official sponsor Mazda.

So now that it has a foot in talent and content creation for brands, what's next for PMK-BNC? Media. Mr. Nyman said the shop is toying with the idea of helping clients more aggressively sell inventory from the digital content they own.