It was formed three years after the demolition of the city's Union Station, during the Urban Renewal movement, with the intention of preventing further such losses.

[1] The company is also the custodian of the Portland Observatory on Munjoy Hill.

As of 2024[update], the president of Greater Portland Landmarks is Bruce Roullard.

[2] In 2024, the company sued the City of Portland in an attempt to prevent the demolition of the building, constructed in 1830, which was formerly the home of the Children's Museum and Theatre of Maine.

[4] The City Council had approved a plan to remove a historic classification from building, which stands in Free Street in Congress Square.