Part of the Watt Institution, the McLean Museum and Art Gallery collection currently contains some 430 oil paintings. This includes a range of works by Scottish, British, European and American artists dating from the eighteenth century onwards.

There are over 300 Scottish paintings by most of the significant Scottish artists working between 1750 and 1950, such as Allan Ramsay, Sir Henry Raeburn, Horatio McCulloch, Waller Hugh Paton, Thomas Fairbairn, William Page Atkinson Wells, William McTaggart, the Glasgow Boys and the Scottish Colourists.

Of particular importance is the Museum's unique collection of works by Inverclyde artists. There are also European and American works in the collection, particularly paintings from late nineteenth- and early twentieth-century America, a legacy of Inverclyde's trading connections with that continent. The McLean Museum and Art Gallery continues to acquire works and seeks to make the collection as widely available as possible.