Triumph Brewery is looking to relocate from the Nassau Street location it has occupied for two decades to the Palmer Square building that was home to the Princeton post office until a few months ago.

Last week, 20 Palmer Square East, the entity that bought the historic post office building in 2013, filed a preliminary site plan with the town to install a 297-seat restaurant and brew pub at that location. David Eichler of the California-based company, and Adam Rechnitz, owner of Triumph Brewery, confirmed Tuesday that Triumph is the operator targeted for the building.

“It’s such a great, prominent building,” said Mr. Eichler. “It presents such an opportunity for this incredible space. Just think about how it can enliven Palmer Sauare.”

Mr. Rechnitz added, “The business [Triumph] has been at 138 Nassau Street for 21 years, and it’s getting a little long in the tooth. It’s time to give it a major facelift. The opportunities are fantastic to think about.” The building contains about 200 seats, he added.

The former post office, built in 1937 and the oldest structure on the square, contains a muralКdone in 1939 entitled America Under the Palms by Karl Free. The mural, which became controversial because of the way it depicts Native Americans, will remain.КThe building includes space not only in the reception area patrons know well, but in the basement and the former mail sorting area. “Most of the public only saw the mail hall area,” Mr. Eichler said. “Behind that the sorting area had ceilings 20 feet high. All of that gets opened up and is part of the layout the architect has worked on.”

The Princeton firms Mills and Schnoering Architects and Richardson Smith Architects have been working on the plan. Mills and Schnoering has been responsible for the exterior, while Richardson Smith has been involved in design for the interior. The plans call for the former loading dock on Palmer Square East to be turned into the main entrance.

“The loading dock has been really pedestrian-unfriendly,” said Mr. Eichler. “Even before we were introduced to Adam, we knew that side of the building had to be reinvented. We had envisioned pulling off the loading dock and creating a new entrance. We wanted to emulate what was there, but re-envision it. What’s interesting to note is that we chose glass for the entrance, because when you take the loading dock off, you’re actually mid-floor of the building. So by creating this glass entry, you bring a lot of light into the building that is missing on what was the mail-sorting side.”

The old entrance to the post office is labeled “special event entry door” on the plans, but Mr. Rechnitz said its function has yet to be figured out. “It’s key to the building. It won’t be secondary,” he said.

Plans filed with the town show 75 seats at the bar, 58 seats in the main dining room, 68 in the “mural dining room,” 58 in the “north dining room,” and 38 on the mezzanine. No outdoor space is planned because the building is on the property line, Mr. Eichler said. “There is no space for that now, but that’s not to say it couldn’t happen in the future.”

Triumph currently has operations in Princeton and New Hope, Pa., and is planning to open another in Red Bank this summer. As for the Palmer Square location, “People will instantly recognize it as one of our properties because the interior design has become such a trademark identified with what we do,” Mr. Rechnitz said. “We’ll be brewing there, updating a lot of the ideas behind it. We’re not really far enough with the menu yet to say much, but I think people will recognize it and like it as they do already.”

The post office building was sold as part of a nationwide downsizing by the U.S. Post Office. Mr. Eichler’s firm, based in California, won the bidding war for the property. The future of the building has been a frequent topic since the sale three years ago. The post office moved to a smaller location behind the 7-Eleven store on East Nassau Street last year.

“I’ve been working with David Eichler, trying to identify tenants for a while,” said Alec Monaghan, first vice president with the real estate firm CBRE. “We’ve been working with a number of interested tenants. We’re thrilled with the prospect of Triumph coming over as the lead tenant. It’s wonderful for the town.”

The application is currently under review. “The staff has to deem it complete or incomplete,” said Mr. Eichler. “We’re waiting to get feedback.”