[1] Maclay began keeping the diary within two months of taking office and kept it almost daily during the 1st United States Congress.

It is one of few accounts of the early United States Senate; sessions would not become open to the public until 1795.

In the diary, which he kept in the evenings, Maclay opined about his colleagues and commented on various issues of pertinence during the period.

It is speculated by some Senate historians that the original incitation for the diary's creation was his somewhat uneasy relationship with the first Vice-President of the United States and President of the Senate John Adams; the two differed sharply on many political issues.

[1] The diary is also included in The Diary of William Maclay and Other Notes on Senate Debates, published in 1988 as part of the Documentary History of the First Federal Congress by the Johns Hopkins University Press.