William Kidner was born on 16 February 1841 at Durston, near Taunton, Somerset, the second son of William Kidner, a farmer and his wife, Ann Smith. The family farmed at Bickley Farm, Milverton, Somerset in 1851. William junior does not appear to have embarked on an architectural career immediately as was working as a builder's clerk in 1861 and at that time was living at 11 Bessborough Gardens, St John's Westminster. His RIBA nomination paper gives no indication of his training but he probably studied at University College London since his proposers were Professor Thomas Leverton Donaldson and his pupil Edward Augustus Gruning; he certainly worked for his third proposer, George Gilbert Scott, as he emigrated to Shanghai in 1864 to build Scott's Holy Trinity Cathedral and set up practice there after it was completed in 1869. His brother had joined him in 1866.
While in Shanghai Kidner visited various places in China and Japan. In his spare time he joined a shooting club and came to be regarded as the finest shot in China. In 1872 William was back in England but returned to Shanghai by Christmas 1873. In about 1874 he engaged as assistant John Myrie Cory, a Carlisle architect who had also been in Scott's office between 1867 and 1869, and had spent fifteen months in the United States in 1870 and 1871. On his return Cory had bought a partnership in the London Roman Catholic practice of a relative Joseph Cory Scholes, but this had apparently not proved a success. In 1875 Cory became a partner in Kidner's Shanghai practice which reached its peak in 1877 with two large bank commissions.
Kidner withdrew from the partnership with Cory early in 1878, as he was in London in March answering questions on Joseph's Conder's paper on Japanese architecture, read at the RIBA by T Roger Smith. In 1877 William Kidner had married Jamesina Nicol Crosbie, daughter of James Crosbie, a bank agent of Elgin and his wife Helen Nicol. They married in Kensington in London. A year later their son, Percy Crosbie, was born. He became a managing director of Vauxhall Motors. They also had a daughter Helen Crosbie. Kidner had met his wife through Jamesina's eldest sister whose husband was John Andrew Maitland. He had made his fortune in the Far East and was head of the Freemason's Lodge (the Northern Lodge of China) to which William belonged. Sometime before 1881 Kidner returned to Britain and settled in Elgin where he designed two large American-influenced houses.
Whether Kidner had visited the USA himself, or had drawn upon Cory's knowledge of American architecture is not clear. The commission for Lesmurdie came through Jamesina's other sister as she had married an Elgin JP, Charles James Johnston. It was for them that William Kidner designed Lesmurdie. In 1884 or 1885 Kidner gave up his Elgin practice and emigrated a second time to design buildings for the British North Borneo Company. Kidner was back in London by 1892 and on 19 November 1894 he read a paper entitled 'Notes upon the architecture of China' written by Frederick M Gratton of Shanghai at the RIBA. Kidner died on 31 March 1900 and is buried at Hampstead Cemetery.