Laszlo Papp was born in Debrecen, Hungary, in 1929. He received a degree in architectural engineering and civil engineering from the Polytechnic University of Budapest in 1955. After graduation, he went to work for the state, which was under Communist rule. Papp worked as an architect for the Institute for Residential Construction, focusing on domestic design. Following his involvement in revolutionary activities, Papp immigrated to the United States in 1956. He earned a Masters of Architecture from the Pratt Institute School of Architecture in 1960. After graduation, he went to work for Harrison & Abramowitz in New York City, remaining with the office until 1963.
Papp moved from Stamford, Connecticut, to New Canaan, Connecticut, in the early 1960s. He purchased a summer cottage in New Canaan in 1959 and expanded and renovated the property, completing the initial phase of work in 1961. It was during this period that he became partner in the firm Millard & Whiteside in White Plains, New York. Over time, Papp took over the office; it was renamed Laszlo Papp & Associates in 1968. The firm's projects include designs for residential, commercial, and institutional buildings. Papp has served as president of the New York State Association of Architects, regional director of the American Institute of Architects, and has been active in several other organizations. In 1981, Papp was awarded membership in the College of Fellows of the American Institute of Architects