Top insurance brokers, No. 6: Alliant Insurance Services

2025 brokerage revenue: $5.72B
Percent increase: 14.4%

Alliant posted another year of double-digit revenue growth in 2025, continuing to hire staff and expand its operations.

Robust growth across several sectors further helped it cement its position as the largest private-equity-backed brokerage.

While mergers and acquisitions also contributed to its expansion, organic growth remains its primary focus, the brokerage’s top executive said.

Alliant reported $5.72 billion in brokerage revenue in 2005, a 14.4% increase over the prior year, which had seen nearly 30% growth. The company moved down one place to No. 6 in Business Insurance’s ranking of the world’s largest brokers, as Brown & Brown jumped to No. 5 following a major acquisition.

Growth in construction insurance, commercial auto liability and its fledgling reinsurance business helped drive the broker to another productive year, said Alliant CEO Greg Zimmer.

“Construction had another great year and reinsurance grew north of 50% last year,” Mr. Zimmer said. “Our nonstandard auto business had another very solid year, so I would say that those would be the three primary growth drivers of the business.”

Its nonstandard auto business is well-positioned, Mr. Zimmer said. “They just continue to outperform. They continue to take market share.”

Alliant, which celebrated its 100th anniversary last year, has grown and diversified substantially over the past several years, said Julie Herman, New York-based director at S&P Global Ratings.

It made its debut in the Business Insurance Top 10 ranking in 2022 and has climbed further up the ranking largely on organic growth.

“They have really grown very, very substantially in a short period of time, and while they do certainly engage in mergers and acquisition, most of that growth has been organically driven,” Ms. Herman said. “It’s been profitable growth as well. It’s not like they’ve grown at the expense of margins.”

Alliant’s issuer credit rating was upgraded to “B+” from “B” by S&P Global Ratings in May, Ms. Herman said. “Alliant Holdings LP’s profitable growth has enabled significant deleveraging in the past year,” she wrote in her upgrade note, which also pegged organic growth at 8.6% for full-year 2025.

Alliant has outperformed its peers “mostly because of the talent that they’ve brought into the organization,” said Chicago-based Timothy J. Cunningham, managing director at Chicago-based investment banking and financial consulting firm Optis Partners.

For years, Alliant has aggressively recruited from rivals, which sometimes led to litigation over alleged breaches of nonsolicitation agreements. This year, however, Alliant was on the other side of the litigation when, like several other brokers, it sued Howden after it hired away several of its staff.

Alliant’s recruitment strategy potentially leaves it in a stronger position moving forward as the inventory of top-tier acquisition targets wanes and overall merger and acquisition activity slows, Mr. Cunningham said.

Future growth is expected from the construction and reinsurance businesses, as well as benefits, Mr. Zimmer said.

“I think construction will continue to outperform the market,” he said. In reinsurance, “we are essentially a facultative-only shop now. We are certainly looking at the treaty side, which would be another big, big opportunity for us.”

In addition, the brokerage’s employee benefits business grew by more than 12% last year, Mr. Zimmer said.

The brokerage had not made any “material” acquisitions in 2025, Mr. Zimmer said. “We made a handful of acquisitions; they were all relatively small, more fold-in, tuck-in type,” but said it had a “robust pipeline” and “some really interesting deals” for the remainder of this year.

Among senior appointments over the past year, Peter Arkley was promoted to president of Alliant’s national retail brokerage, a new role created to manage the broker’s growth, Mr. Zimmer said.

Mr. Arkley was succeeded as president of Alliant’s property and casualty division by Michael J. Cusack, who previously served as head of Alliant Specialty.

Artificial intelligence presents Alliant with opportunities to “create efficiencies within our organization,” Mr. Zimmer said, but he dismissed the specter of “disintermediation” for complex commercial risks.

“At the end of the day, the client wants to look to someone to provide them with an educated decision, and I don’t see that changing anytime soon,” Mr. Zimmer said.