The official who has spearheaded Mayor Muriel Bowser's affordable housing strategy since she took office in 2015 is retiring.

Polly Donaldson, the director of D.C.'s Department of Housing and Community Development, will retire at the end of this month, she announced Friday.

Donaldson, who retires as the longest-serving director of DHCD, managed the District's Housing Production Trust Fund, its main vehicle for financing affordable housing. The District has used the fund to invest $600M in affordable housing projects since 2015, DHCD said.

The District has financed 14,250 units of new affordable housing construction and has preserved more than 1,500 units since 2015, DHCD said. It has another 12,300 new affordable units in the pipeline.

Along with the announcement, DHCD said the city is on track to meet Bowser's 2019 goal of creating 36,000 new housing units by 2025, with at least 12,000 of them affordable. To help reach that goal, Bowser increased the Housing Production Trust Fund allocation in this year’s budget from its original level of $100M annually to $400M over the next two years combined.

“When I came into office and committed to investing at least $100M into the Housing Production Trust Fund every year, I knew we would need a leader with a true passion for affordable housing to get those funds out the door and into our community — and Polly was the right person for the job,” Bowser said in a release.

Donaldson also worked to expand D.C.'s partnership with the U.S. Department of Housing and Urban Development. HUD announced in February it would guarantee a $38.8M loan to DHCD to fund the rehabilitation of affordable housing properties in D.C.

HUD Deputy Assistant Secretary for Grant Programs Kevin Bush, speaking alongside Donaldson at a Bisnow event on Aug. 25, said the program is a model he would like to see replicated across the country. Donaldson said the partnership allowed her agency to use more of the money in D.C.'s affordable housing fund to finance new development.

“What this does is enable us to maintain and preserve our existing affordable housing, meaning we can use more of our Housing Production Trust Fund dollars toward production of net new units in the District,” Donaldson said at the event.

During her time as DHCD director, Donaldson served as co-chair of the D.C. Interagency Council on Homelessness' Housing Solutions Committee. She has also served as co-chair of the Metropolitan Washington Council of Governments' Housing Directors Advisors Committee, and she has been involved with other regional and national housing organizations.

Prior to joining DHCD, Donaldson spent 10 years as executive director of the Transitional Housing Corp., according to her LinkedIn page. Before that, she worked at the Institute of International Education and at Partners of the Americas.

The Bowser administration hasn't announced who will replace Donaldson at the helm of the 180-person agency when she leaves at the end of the month.