Mary Sue Butch has been actively involved in securitization since its beginnings in the mid-1980s. 

Before becoming a securitization lawyer, she practiced tax law with a focus on tax issues affecting securitizations. She participated in the creation of the first residential CMOs, REMICs, auto, lease, floor plan, student loan and credit card securitizations, CDOs, synthetic structures, and other asset-backed financings, such as catastrophe bonds, asset-backed commercial paper, medium-term note programs and repurchase agreements.

Mary has executed dozens of residential loan private and public securitizations with both agency and whole loan collateral, and negotiated various guarantee and reserve fund arrangements to guard against any special hazards not covered by conventional homeowners' insurance. She was part of a team that acted as designated underwriters' counsel in the Resolution Trust Corporation's residential mortgage loan securitizations, as well as underwriters' counsel on many of the RTC's commercial and "nonperforming" loan securitizations. Mary has advised mortgage REITs and structured mortgage loan securitizations.

She has represented issuers and underwriters in securitization of commercial loan portfolios, including non-uniform portfolios of underperforming loans. Since 2003, she has been part of a team of real estate finance lawyers structuring large commercial mortgage and mezzanine loans, most intended for securitization, tranching such loans into multiple notes and participations for sale to investors, and modifying such loans and related transactions as and when necessary as well as arranging financing for loans and CMBS, such as repo lines and lines of credit.