Penelope Alice Marjorie Seidler AM (nee Evatt, born 15 December 1938) is an Australian architect, former member of National Gallery of Australia Council, and current member of the NGA Foundation Board. She is also an accountant and director of the Sydney-based architectural firm Harry Seidler and associates. She was the wife and professional partner of architect Harry Seidler. She was the subject of the 2014 Archibald prize winning portrait by Fiona Lowry.
 Penelope grew up in Wahroonga, New South Wales, daughter of Clive Evatt (1900–1984), a prominent barrister and NSW Labor politician (MLA for Hurstville 1939–1959), and his wife Marjorie Hanna Evatt (née Andreas) (1903–1984), with two siblings, Elizabeth Evatt and Clive Evatt jr. The Evatt family home located at 69 Junction Road, Wahroonga is now known as "Parklands" and is listed on the NSW State Heritage Register.
 Seidler is the director of Sydney-based architectural firm Harry Seidler and Associates.
 She studied for her Bachelor of Architecture at the University of Sydney and was registered as an architect in 1964. She joined Seidler and Associates that year as architect and financial manager. She has been a Fellow of the Australian institute of Architects since 1983, sitting on the NSW executive council from 1982 to 1984.
 She was a founding member of Chief executive Women (NSW) from 1990 to 2005.
 She currently sits on UNSW's Faculty of the Built Environment advisory council.
 Penelope Seidler has sat on the International Council of the Museum of Modern Art in New York since 1973, has been a Biennale of Sydney director since late 2010, and was deputy commissioner for the Australian Pavilion at the 2013 Venice Biennale. She was an International Advisory Board member of Vienna's Austrian Museum of Applied Arts/Contemporary Art, and is a former council member of the Australiana Fund.
 In 1971 Seidler joined the Art Gallery of NSW Society's council being one of the first "volunteer guides".
 In 1973, Seidler received an offer letter from New York's Museum of Modern Art requesting her to be one of the members of its International Council.
 In 2008 she became the Member of the Order of Australia for her work in the visual arts and architecture. In 2011, she was made a Chevalier of the Légion d'Honneur by the French government and received an honorary Doctor of Letters from the University of NSW.
 In 2018 Seidler made a gift to the University of Sydney to establish the Penelope Visiting Professorship in Architectural History. The inaugural Penelope Professor was the French architectural historian Jean-Louis Cohen who spoke on the theme of "Frottage City".
In 2021, the University made her an honorary Doctor of Architecture.
 Penelope met Harry Seidler in 1957 at a fellow architect's drinks in North Sydney. They married on 15 December 1958, and had two children.  Together they lived in Point Piper, in a basement apartment on the water for just over one year, afterwards they moved to Ithaca Gardens, Elizabeth Bay, a newly completed Seidler apartment building, and lived there from January 1960 until late June 1967 before moving to the Harry and Penelope Seidler House, designed by her and her husband, located in Kalang Avenue, Killara on Sydney's North Shore.