Harry John Charles Diddams (26 April 1864 – 11 March 1929) was a master printer and politician in Brisbane, Queensland, Australia. He served two terms as Mayor of the City of Brisbane before its amalgamation with surrounding local authorities into Greater Brisbane in 1925.
Harry Diddams was born on 26 April 1864 to John William Diddams and Lydia Mary (née Flower) at Coniston Cottage, Parnell in Auckland, New Zealand. Although he was described in a report of his wedding as "the second son", NZ birth records indicate that he was the eldest of three children.
He married Henrietta (Hettie) Gibbs Hicks, third daughter of the late Robert McCall Hicks, on 17 April 1895 at All Saints Church, East St Kilda, Victoria.
Harry served his apprenticeship as a compositor on the Auckland Star in his home city. In 1881, he moved to Melbourne where he joined the printing firm of McCarron, Bird & Co.
Harry Diddams first attempt to enter local politics came in January 1907 when he opposed the sitting alderman in the South Ward of the Town of Toowong where he was living in Ashton Street. The incumbent was returned comfortably.
In August 1907, a casual vacancy arose on the Brisbane Municipal Council through the resignation of the Alderman for West Ward. Although still resident in Toowong, Diddams was qualified as the owner of a business in Brisbane's business district (Adelaide Street), was nominated by several prominent businessmen and appointed by Council. He remained an alderman from 1907–1921 and served on many of the Committees of Council. Harry Diddams served two terms as Mayor of Brisbane; first in 1911 and then 1921–1924.
The first term, during which Diddams also served as President of the Local Authorities Association of Queensland, coincided with the Coronation of King George V. When he was named a Companion of the Order of st Michael and St George in the New Year's Honours List of 1912, His Worship explained that "the citizens of Brisbane are honoured equally" and "every local authority member ... participates in the honour paid to me". A columnist on the Truth offered a more cynical view.