As the eldest of eight siblings, Finley provided financial and moral support to an extended family in South Carolina and elsewhere after his father died in 1917 and throughout his own life.
Upon their return in 1933, Mellon was forced to spend most of the next three years defending himself, against politically motivated charges of tax fraud brought by the Roosevelt administration, while Finley continued to work on planning the National Gallery.
In late 1936 Finley selected twenty-four Italian Renaissance paintings and eighteen sculptures from Lord Joseph Duveen, which Mellon bought to complete his collection.
Finley's skills in dealing with the government had been honed by thirty years in Washington and he got chief Justice Harlan Fiske Stone and President Franklin D. Roosevelt to champion their cause.
Although wartime Washington had greater priorities than cultural protection in Europe, Finley persuaded the administration to appoint, in August 1943, the American Commission for the Protection and Salvage of Artistic and Historic Monuments in War Areas, a blue ribbon panel of distinguished civilians led by Associate Justice Owen J. Roberts as chairman.
Acting in close concert with the War Department, which placed over two hundred Monuments and Fine Art Officers in the field, and similar Allied groups, the Roberts Commission oversaw the rescue of most of the threatened artworks of war-torn Europe.
As chairman of its trustees, Finley led the National Trust through its critical early years, when the concept of the preservation of old buildings was considered a novel and radical departure from prevailing views.
Finley's dual roles as chairman of the Fine Arts Commission and the National Trust for Historic Preservation gave him access to Presidents Truman, Eisenhower and Kennedy.
Jacqueline Bouvier Kennedy and Finley formed a powerful team for the promotion of good taste in monumental Washington and the White House and they became close personal friends.
David Finley took up the cause and in 1956 when the federal government planned to demolish the Old Patent Office Building, one of Washington's oldest and most beautiful, for a parking garage, Finley as chairman of both the National Trust for Historic Preservation and the Fine Arts Commission, appealed to President Dwight D. Eisenhower, who saved it for the National Portrait Gallery.
David and Margaret Finley presented one of the first pieces of fine antique furniture to the White House, an example soon followed by many other prominent Americans.
[5] In over 60 years in official Washington, David Finley mastered the Capital's twin arts of the political process and social life.
As J. Carter Brown, one of Finley's successors at the National Gallery of Art and the Commission of Fine Arts and himself an expert in the field, once put it, “If anyone ever knew how things get done in Washington, it was David Finley.” Finley was a gifted writer and from 1913 to 1930 kept a series of journals that expressed his views on a wide range of personal matters and public affairs.