Mark was born on November 7, 1967 to Charles and Janice Poloncarz, each now retired as a steelworker and nurse from Bethlehem Steel Corp. and Mercy Hospital, respectively. The eldest of three sons, Mark grew up with his parents and younger brothers Robb and Kevin in the blue-collar steel town of Lackawanna, New York. Mark graduated as a National Honor Society Member and Regents scholar from Lackawanna Senior High School in 1985 and received a Bachelor of Arts Degree from the State University of New York at Buffalo in 1989.

After working in the private sector for five years Mark then attended from the University of Toledo College of Law, graduating in 1997. During his final year of law school Mark won the University of Toledo’s moot court competition and received the prestigious “Barrister” award honoring his accomplishment.

Passing the New York State Bar exam on his first attempt, Mark then practiced corporate and finance law in Buffalo, New York and was last associated with the firm of Kavinoky Cook LLP. His legal practice included representing businesses, both large and small, and local governmental authorities during complex public and private mixed finance transactions.

Active in his community, Mark served on numerous not-for-profit corporate boards as both a director and an officer and has a solid history of guiding financial distressed institutions to solvency.

Since taking office on January 1, 2006, Mark has dedicated his administration towards creating a more efficient comptroller's office and restoring fiscal stability to Erie County's government. He has released more financial statements and reports than any of his predecessors, including issuing for the first time comprehensive and detailed quarterly reports on Erie County's finances. These reports have helped the county executive, legislature, Erie County Fiscal Stability Authority and Wall Street better understand the issues facing Erie County. Quarterly reports on financial conditions are standard in the private sector, and have become the norm in Erie County during Mark's term in office.

He has also strengthened the office's Audit Division by conducting timely, proactive and thorough audits and reviews of Erie County's departments, related entities and issues facing Erie County's residents. He has shaped the Audit Division into an Inspector General-style organization that stops and prevents waste, fraud and abuse of county taxpayers' dollars, and was honored for his efforts when the Association of Local Government Auditors gave his office its prestigious 2007 Bronze Knighton Award for small audit departments. His office was the first municipal government auditor in New York State ever to receive any Knighton Award.

While he has acted as the taxpayers' watchdog and called out wasteful spending and irresponsible actions, he has worked collaboratively and cooperatively with the county executive, legislature, and the Erie County Fiscal Stability Authority in order to restore fiscal discipline to county government.

Mark resides in the City of Buffalo with his wife Elizabeth.