Horace was born in Sydney, New South Wales on Friday, 21 February 1879, the third son of Samuel Thomas Whiddon and Kate Gertrude Fogorty. He was one of seven children, having three brothers and three sisters.

Horace and his next older brother, Frank formed Whiddon Bros, a wool-scouring business in January 1900. The business was established at Botany, New South Wales. In 1906, their business acquired Messrs Johnson’s and Vicars’s works on the water reserve at Botany. They were joined at some time by their eldest brother, Arthur.

Whiddon Bros Ltd became a public company in January 1910 with authorized capital of £50,000 in £1000 shares. Frank served as chairman and managing director. Arthur served as secretary. The business expanded to include wool combing and fell-mongering in 1911. The business continued to expand with the acquisition of the adjacent Bridgewater Wool Scouring Co. in about 1938. The company also entered into an arrangement with Buzacott & Co. Ltd for the Lan-O-Leen Co. to produce sheep dip, agricultural sprays and the sheep feed on their site. By this time Frank and Horace had gained control of the assets of the firm which was reconstituted as Whiddon Pty Ltd.

Horace married Lillian Curnow on Saturday, 25 July 1908 and had one son.

Horace was the member of the NSW Legislative Council for Croydon from 27 September 1934 to 22 April 1955 – a term of 20 years 6 months 27 days.

Horace was a member of the National Party, the United Australia Party and later the Liberal Party. He was president of Parkes Federation and Croydon state electoral councils.

His qualifications, occupations and interests include the following:
Wool merchant. Educated at Fort Street High School; served five years apprenticeship in wool scouring establishments; established the firm of Whiddon Brothers with his brother in 1900; later became managing director of Whiddon Pty Limited, wool manufacturers and exporters; executive member of Royal Agricultural Society; trustee of National Park 1933-1949, president 1934-1949; director of Royal Prince Alfred Hospital 1934-1955; life member of New South Wales Rugby Union; local president of Boy Scouts' Association; member of New South Wales Wool Committee.

Information from this biography was extracted in part from G. P. Walsh, ‘Whiddon, Frank (1877—1947)’, Australian Dictionary of Biography, National Centre of Biography, Australian National University, published first in hardcopy 1990, accessed online 13 November 2021.