The Brookline Reservoir property is a dammed pond approximately 1 mile in circumference. A jogging and walking track encircles the reservoir. The entire park is visible from virtually the entire perimeter, while the details of the property become observable when walking along the circular path. The architecturally significant gatehouse is a prominent feature. Most of the park is set below the surrounding roads, creating a feeling of separation between the park and abutting lands. Swimming and skating are not allowed on the property. The reservoir is on the National and State Registers of Historic Places. The reservoir is stocked annually with fish by the Massachusetts Department of Fish and Wildlife. Fishing is allowed by permit from the Town Clerk's Office.

The reservoir was originally built as a drinking water supply for the City of Boston. This area was once low-lying pasture land with a marsh in the center and a stream running through it. The reservoir was part of the Cochituate water system and was built to feed the Beacon Hill Reservoir that stood at the intersection of Hancock, Derne, and Temple Streets. The Brookline Reservoir was filled in 1848. Its granite gatehouse has the oldest extant iron roof in the United States, supported by the oldest extant wrought iron roof trusses in the United States, and it houses the oldest cast iron staircases in the United States intended for public use.

In 1902, the City of Boston decided to sell the reservoir and its surrounding land. Prompted by rumors of undesired development, the neighbors, including Amy Lowell, John C. Olmsted, Walter Channing, Edward Atkinson, and George Lee, contributed more than $50,000 towards the purchase price of $150,000.

In 1926, the gatehouse interior was altered to provide rooms and toilet facilities for swimming meets, skating, and other occasions, and a pier was built nearby. A 1945 plan to build a beach and bathhouse near Lee and Dudley Streets was never realized. The Reservoir Park was considered briefly in 1956 as a possible location for a new Town Hall.

The land was purchased from the City of Boston with the condition to "operate and maintain to flow water through." The property is individually listed on the State and National Register of Historic Places and as part of the Cochituate Aqueduct Linear National Register District.