WilliamsMarston Welcomes Marcello Castellano as Finance as a Service Practice Leader

Castellano Joins the Accounting, Tax, Technology, Transaction and Valuation Advisory Firm to Spearhead New Offering for High-Growth and Early-Stage Companies

BOSTON--(BUSINESS WIRE)--Marcello Castellano has joined WilliamsMarston as Partner and Finance as a Service (FaaS) Practice Leader, based in its Boston office. His appointment marks the formal launch of WilliamsMarston's new Finance as a Service practice, which will deliver end-to-end finance and accounting capabilities through a technology-enabled platform model.

The new practice will provide clients with a full outsourcing model for operational and strategic finance and accounting capabilities and supports high-growth and early-stage companies seeking to scale their finance operations efficiently without adding significant internal headcount or infrastructure.

“Marcello brings the ideal combination of technical accounting expertise, operational finance experience, and deep familiarity with the needs of high-growth companies,” said Sanjay Ramaswamy, Chief Executive Officer. “As companies continue to look for more efficient and scalable ways to build their finance functions, our Finance as a Service practice will provide clients with the capabilities, infrastructure, technology and support they need at each stage of growth. We are excited for the impact Marcello will make in this new role.”

As Practice Leader, Castellano will focus on building the foundation of the FaaS practice, expanding WilliamsMarston’s capabilities in outsourced finance and accounting support, and helping clients develop scalable finance operations that support long-term growth.

“I’m excited to lead a practice that directly addresses the needs of companies as they scale,” said Castellano. “High-growth businesses need strong finance and accounting capabilities, but they do not always need or are not always able to build a full internal function right away. FaaS, with the right foundation of AI-enabled technology, gives them a model that can grow alongside them while also providing the rigor and support they need to operate with confidence.”

Castellano brings more than 20 years of experience advising high-growth and emerging businesses across finance, accounting, and business transformation. He joins WilliamsMarston from Browne Consulting, where he spent six years advising venture-backed and emerging life sciences companies on operational accounting and strategic finance.

Earlier in his career, Castellano spent several years at PwC, including time in the firm’s Global Capital Markets group in Europe and its Transaction Advisory practice, where he focused on private equity buy-side diligence and complex capital markets matters. He also previously spent nearly four years at WilliamsMarston as a Managing Director, working with clients on technical accounting, financial reporting, and business transformation matters.

About WilliamsMarston

WilliamsMarston is a national accounting, tax, technology, transaction, and valuation advisory firm serving pre-IPO, public, and private equity-backed companies managing rapid growth and transformation. With 300 professionals, the firm combines deep technical expertise with practical experience—including leadership from the Big Four—to help clients navigate their most complex and high-stakes challenges. For more information, please visit https://williamsmarston.com/ and follow WilliamsMarston on LinkedIn.