Grant Thornton announces new leader for its Chicago headquarters


CHICAGO — Grant Thornton LLP, one of America’s largest providers of audit and assurance, tax and advisory services, has announced a new leader for the Chicago market. Arla Lach, an Audit and Assurance partner who has been with Grant Thornton nearly 25 years, will succeed Mark Sullivan. Sullivan is retiring after a successful, decades-long career, including more than 14 years with the firm.


Lach and Sullivan are working closely to ensure a seamless transition, and Lach’s term as market managing partner will officially begin on June 1. Between Grant Thornton’s Chicago and Downers Grove offices, she will lead nearly 1,000 professionals, helping them provide personalized, high-quality service to the firm’s clients across the country.


She assumes this new role at an exciting time for the firm: Grant Thornton will celebrate its 100-year anniversary this summer.


David Platt, Grant Thornton’s Central region managing partner, looks forward to working alongside Lach as the firm builds on multiple years of record-breaking growth and the momentum of its upcoming centennial.


“Arla has been an integral part of Grant Thornton’s growth in Chicago, and she knows how to build and strengthen high-performing teams,” Platt said. “It’s extremely rare for businesses to reach 100 years, and it only happens if they have people like her moving the team forward. I know she’ll be a catalyst for even more growth in the years ahead.”


Nichole Jordan, the firm’s national managing partner of Geography, adds that Lach is “the right leader at the right time.”


“From her unparalleled client service to her knack for mentoring and motivating our people, Arla has made a tremendous impact on our firm and our Chicago headquarters,” Jordan said. “I’m looking forward to working alongside her as we drive more growth in the Chicago market and provide truly distinctive experiences to our clients across all industries.”


Lach joined the firm in 1999 and has spent her entire career at Grant Thornton. She has served in a succession of leadership roles, including a two-year appointment as chief of staff to the CEO, during which time she worked alongside the chief executive and other senior leaders to grow the firm’s business.


She also served as the Audit practice leader for the Chicago office, and most recently, she was the firm’s Midwest Geography leader, overseeing audit work for all clients served by the firm’s teams in Chicago, Minneapolis and Wisconsin. In this role, she helped the firm attain multiple years of record revenues while helping clients successfully navigate the challenges posed by the COVID-19 pandemic and the supply chain crisis.


Her accomplishments in these major leadership roles helped Lach win a 2022 Notable Gen X Leader in Accounting award from Crain’s Chicago Business. Lach’s appointment also makes her the first woman to lead Grant Thornton’s Chicago office — advancing the firm’s recent DE&I progress. Forty percent of Grant Thornton’s partners, principals and managing directors are now women or come from diverse demographics, including people of color, LGBTQ+ people, individuals with disabilities, and veterans or military spouses. 


Lastly, Lach’s industry experience spans an array of sectors, including manufacturing, distribution, technology, life sciences and professional services. Sullivan has seen firsthand how this industry knowledge benefits Lach’s colleagues and the firm’s clients.  


“As part of my Chicagoland leadership team, Arla has spent the last three years epitomizing what it means to be a professional services leader in the new era of our industry,” Sullivan said. “She has the invaluable ability to translate industry knowledge into strong and effective strategies, and just as importantly, she is the kind of compassionate, people-focused leader that professionals love to work with.”


In turn, Lach is eager to praise Sullivan, who previously served on the firm’s Partnership Board and spent decades helping businesses navigate complex regulatory matters.


“Mark and our incredible Chicago team have helped Grant Thornton expand our footprint in both Chicago and across the country, and we’re going to continue what we’ve started,” Lach said.


She concluded: “As a lifelong Chicagoan, I take immense pride in providing our city’s businesses a level of service they can’t get anywhere else. That’s why I’m eager to help our talented professionals exceed our clients’ expectations in every way possible.” 


Lach earned a bachelor’s degree in accounting from the University of Illinois Urbana-Champaign.

About Grant Thornton LLP

Grant Thornton LLP (Grant Thornton) is one of America’s largest providers of audit and assurance, tax and advisory services — and the U.S. member firm of the Grant Thornton International Ltd global network. We go beyond the expected to make business more personal and build trust into every result. With revenues of $2.4 billion for the fiscal year that ended July 31, 2023, and almost 50 offices nationwide, Grant Thornton is a community of more than 9,000 problem solvers who value relationships and are ready to help organizations of all sizes and industries create more confident futures. Because, for us, how we serve matters as much as what we do. 


“Grant Thornton” refers to Grant Thornton LLP, the U.S. member firm of Grant Thornton International Ltd (GTIL). GTIL and the member firms are not a worldwide partnership. Services are delivered by the member firms. GTIL and its member firms are not agents of, and do not obligate, one another and are not liable for one another’s acts or omissions.




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