Portland Design Team, the predecessor firm of PDT Architects, was envisioned by two college roommates who shared the same vision of a design-oriented, diversified architectural practice. Having worked for large architectural firms specializing in education, David C. Webster and Lyndon D. Keck relocated from Cambridge, Massachusetts, to Portland, Maine, in the mid-1970s. Portland Design Team was anchored in 1977 on Exchange Street in the city's redeveloping Old Port.

Within five years the firm was recognized for having successfully completed a myriad of historic renovations with a bent for interior design and adaptive re-use. In 1985, the firm moved to the Victoria Mansion Carriage House and nurtured the restoration of their new home. The new office quickly became a historic landmark as well as a magnet for talented architects.

Portland Design Team continued its quest for a diversified practice and developed a specialty in designing programmatically complex and highly imaginable buildings including educational and health care facilities, retail stores, and offices. Alan G. Kuniholm, who had been practicing architecture in western Massachusetts and teaching at UMass, joined the firm in 1984. As a creative design leader, Alan was made a principal in 1994. Brian M. Curley joined the firm in 1996 and was made a principal in 2003, expanding PDT's presence in housing, retail, and commercial design. Ann M. Fontaine-Fisher, an established leader in health care design, joined the firm in 1999 and was made a principal in 2003.

In 1996, the firm relocated to 49 Dartmouth Street in Portland, adjacent to Back Cove, to provide better access for their clients and staff.

PDT Architects has attained a current size of twenty-five employees, including five principals and five associates, and enjoys a diversified practice throughout New England. The principals remain committed to the highest levels of sustainable design, personal service, and professional development in designing buildings that strengthen communities and enrich our lives.