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Walter Hillier was born in Hong Kong and educated at Bedford School and at Blundell's School in Tiverton. His father was Charles Hillier, British Consul at Bangkok and his mother, Eliza, daughter of the well-known missionary, Walter Henry Medhurst. He was the brother of Edward Guy Hillier, one of the most respected bankers in the Hong Kong & Shanghai Bank and its long-term manager in Peking (1889-1924).
- 1867: Appointment to the Consular Service and service as an interpreter in China (followed by various promotions)
- 1879: Assistant Chinese Secretary in Peking (in 1883 accompanying Sir Harry Parkes to negotiate the treaty with Korea
- 1885: Chinese Secretary
- 1889–1896: Consul-General in Seoul.
Hillier retired in October 1896 and from February to April 1901 was attached to the Legation in Peking as special political officer for Chinese affairs with the rank of acting First Secretary in the Diplomatic Service. This involved his appointment as adviser to the military authorities in China at which time he was Mentioned in despatches. A stone memorial was erected to Hillier and to a British military officer at Shan-hai-Kwan to recognise the protection afforded to Chinese during the times following the Boxer Rebellion. From 1904–1908 Hillier was Professor of Chinese at King's College London. From 1908–1910 Hillier served as an adviser to the Chinese government, in particular advising Li Hung-chan during his time as Viceroy of Zhili.
- A Progressive Course Designed to Assist the Student of Colloquial Chinese as Spoken in the Capital and the Metropolitan Department (1886), with Thomas Francis Wade; 語言自邇集 (Yü yen tzŭ êrh chi)
- The Chinese Language and How to Learn It: A Manual for Beginners (1907)
- One Thousand Useful Chinese Characters (1907)
- An English-Chinese Dictionary of Peking Colloquial (1910)
- English-Chinese Pocket Dictionary of Peking Colloquial (1910)
- Memorandum Upon an Alphabetical System for Writing Chinese: the Application of this System to the Typewriter and to the Linotype or other Typecasting and Composing Machines and its Application to the Braille System for the Blind (1927)
Hillier drafted the preface to Isabella Bird Bishop's 1898 book, Korea & her Neighbours: A Narrative of Travel, with an Account of the Recent Vicissitudes and Present Position of the Country.
- "Death of Sir Walter Hillier," The Times (UK). 11 November 1927, p. 18.
- "The Late Sir Walter Hillier," The Times 17 November 1927, p. 16.