Kostantinos focuses his practice on corporate and securities law, commercial lending, and capital markets transactions, including financings. He has experience drafting and negotiating purchase agreements and other documents for debt offerings, acquisition financing bids, and credit agreements as well as preparing loan documents for secured and unsecured loans. Kostantinos represents public and private companies in a variety of industries, including investment banks and other financial services firms.

Prior to joining Mintz, Kostantinos was an associate and summer associate at a New York–based international law firm, where he worked on various aspects of financings and capital market transactions.

While attending law school, Kostantinos served as a judicial intern for the Honorable Jack B. Weinstein of the US District Court for the Eastern District of New York. In law school, Kostantinos served on the Fordham Urban Law Journal and as interschool competitions editor for the Fordham Moot Court Board. He was also the student representative to the Fordham Law Long Range Planning Committee.