In more ways than one, the past 12 months could aptly be described as a transitional period for Willis Group Holdings P.L.C.

Since July 2012, the London-based brokerage has undergone substantial changes in its senior leadership, most notably at the chief executive level: Dominic Casserley, a former senior partner at McKinsey & Co., succeeded Joseph Plumeri as CEO of Willis in January 2013.

Additionally, the company within the past year has nominated four new members to its board of directors, as well as appointed new CEOs to its North America segment and several business units within its international and global segments.

Amid the executive-level personnel changes, analysts said Willis' financial results in 2012 were underwhelming by most standards. However, they noted the company's performance in its last two reported quarters bore some signs of improvement, particularly in the troubled North America segment.

Willis' brokerage revenue in 2012 totaled $3.46 billion, a mere 1.3% increase from totals recorded in 2011, but still good enough to keep the company at No. 3 in Business Insurance's 2013 ranking of the world's largest insurance brokers.

Willis' “results have been very, very mixed, but one thing that stands out to me is the recovery on organic growth that began in the fourth quarter of last year, where it had been moderately positive but below average year after year,” said Meyer Shields, a Baltimore, Md.-based managing director of equity research for property/casualty insurance at Keefe, Bruyette & Woods Inc.

Willis reported gross revenue increases of 6.3% in the fourth quarter of 2012 over the prior-year period, including 7.5% organic growth across its major operating segments. Through the first three months of 2013, gross revenues increased 3.5% over results from the first quarter of 2012, including 4.1% organic growth companywide.

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Mr. Shields said the turnaround in Willis' overall organic growth likely reflects a clearer view of the company's operational performance, absent certain nonrecurring revenue streams such as the unsustainable spike in business within the North America segment's loan protector unit, as well as fraudulently overstated revenue disclosed last year.

“When they stopped having to compete against those unrealistic historical numbers, that it made it easier for the company to grow,” Mr. Shields said.

The 1.3% gain in commercial brokerage revenue was driven largely by 6% organic growth within Willis Global, the company's reinsurance arm.

Organic growth within Willis' international brokerage rose 5% in 2012, but was offset nearly entirely by negative foreign currency translation, resulting in flat total revenue for the segment.

Willis' domestic retail segment, Willis North America Inc., saw its total revenue for 2012 decline by roughly 1% compared with the prior year, as did organic growth.

However, analysts noted that results for the North America segment appeared to be rebounding during its two most recent reporting periods, compared with its performance through much of 2011 and 2012. The segment's fourth-quarter brokerage revenue increased 4.7% over the same period in 2011, including 5% organic growth.

“Going back to 2011, we started focusing with a great deal of intensity on some basic tenets of the business and really working hard on new business and pipelines, recruiting and retentions,” said Victor Krauze, chairman and former CEO of Willis North America. Todd Jones, the segment's president, was selected to succeed Mr. Krauze as CEO on July 1.

“It's a big ship and it takes a while to turn, but you're seeing the fruits of those labors come to pass,” Mr. Krauze said.

In the first quarter of 2013, Willis North America grew its brokerage revenue by 4.9% compared with the prior-year period, including 4.3% organic growth, outpacing Willis' other operating segments. Analysts said the improved results were encouraging, though it remains unclear if they are indicative of a long-term correction for the segment.

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“After disappointing for a while, it's been nice to see the turn in the retail segment. It's far too early to declare victory, but they have been able to string together two quarters in a row of solid organic growth out of North America,” said Gregory Locraft, a Boston-based executive research director at Morgan Stanley & Co. L.L.C.

“They're retaining producers, and they're winning more business than they're losing, and they're definitely benefiting from an improving economy in the United States and, particularly, what seems to be some improvement within the small and midsize sector,” Mr. Locraft said.

While Mr. Casserley has yet to formally unveil a long-term strategy for Willis going forward — the company has said he intends to do so at its investors' day on July 25 — other senior executives said his background in management consulting has brought fresh perspective to the company's operations.

“It's a significant change for the organization,” said Steven Hearn, who was named the company's deputy CEO in October. “Dominic arrives with an obvious understanding of how to do strategic work, a very team-based style, and he's very adept at partnering and collaborating with people who bring different experiences and different contributions to the debate. That's the sort of dynamic that's evolved as he's come in, and there's a sense of excitement around the place.”