He was born in the Södermalm district in central Stockholm, Sweden as the second son of a primary school teacher, August Hallström, and his wife Hilda. His eldest brother was the artist Gunnar August Hallström (1875–1943). His youngest brother was the archaeologist Gustaf Hallström (1880–1962).
In 1893 he joined the Merchant Marine and sailed on three ships before going ashore in Cape Town, South Africa during December 1895. He joined the Cape Mounted Rifles in South Africa as a Private in 1897. Between 1897 and 1919, Thord-Gray participated in 13 different wars covering several continents.
He changed his name to Gray in 1899 and Thord-Gray 1917. In 1923, he wrote a book about Mexican archeology Från Mexicos forntid : bland tempelruiner och gudabilder.
In 1925 Thord-Gray moved to the United States and established I.T. Gray & Co, an investment bank located at 522 Fifth Avenue in New York City. He became a citizen of the United States during 1934. He was married to Josephine Toerge-Schaefer (1925–1932) who had two children, Edward and Frances. He was subsequently married to Winnifred Ingersoll (1933–1960). In 1929, he established residence at Gray Court in Belle Haven in Greenwich, Connecticut. In August 1935 he was appointed Major-General and Chief-of-Staff to Governor David Sholtz of Florida.
In 1955, he wrote Tarahumara-English, English-Tarahumara dictionary and an introduction to Tarahumara grammar. (Coral Gables, Fla., University of Miami Press, 1955). He also wrote a book about his experiences in the Mexican Revolution, Gringo Rebel: Mexico 1913–1914 (Coral Gables, Fla. : University of Miami Press, 1961). In later years he had his winter home in Coral Gables, Florida.
- Worked as a Prison Guard on Robben Island 1896
- In 1897 he enlisted in the Cape Mounted Riflemen and fought the Boer War 1899–1902
- Served in the South African Constabulary 1902–1903
- Transvaal Colony Civil Service 1903–1906
- Captain in the Lydenburg Militia 1904
- Joined Royston's Horse as a Lieutenant and fought in the Bambatha Rebellion 1906 being promoted Captain.
- Captain of Nairobi Mounted Police 1907
- Captain Philippine Constabulary ("US Foreign Legion") 1908–1909
- Planter in Malaya 1909–1911. Served a short time in the Chinese Revolution 1913
- Joined Mexican Revolution as Captain and Commander of Pancho Villa's artillery 1913
- Promoted Major, Lieutenant-Colonel and Colonel 1914
- Chief of Staff 1st Mexican Army 1914
- Joined British Army 1914 as a Major and second in command of 15th Bn Northumberland Fusiliers
- Lieutenant-Colonel and Commanding officer of 11th Battalion Northumberland Fusiliers 1915, 1/26th Battalion Royal Fusiliers 1916
- Awarded 1914-15 Star, British War Medal, and Allied Victory Medal
- Lieutenant-Colonel Canadian Expeditionary Force (CEF-S) to Siberia 1918
- Transferred to Russian "White" Army February 1919 as Colonel
- Commanding Officer of 1st Siberian Assault Division
- Major General November 1919 and High Representative of the Provisional Siberian Government to the Allied Expeditionary Corps in Vladivostok
- Ivor Thord-Gray (Great War Forum)
- Gustaf Hallströms fotografisamling (Forskningsarkivet)
- Thord-Gray, Ivor (1923). Från Mexicos forntid: bland tempelruiner och gudabilder (in Swedish). Stockholm: G. Tisells tekn. förl.
- The London Gazette: . 24 November 1914. Retrieved 2007-10-31.
- The London Gazette: . 22 February 1916. Retrieved 2007-10-31.
- "Library and Archives Canada". Retrieved 2007-07-23.
- Thord Ivar Hallströms handlingar - Some 1,000 letters and documents regarding Ivor Thord-Gray deposited in the Kungliga Biblioteket in Stockholm
- Bojerud, Stellan Ivor Thord-Gray - Soldat under 13 fanor (Sivart Förlag AB, Stockholm. 2008) ISBN 91-85705-13-6
- Gyllenhaal, Lars & Westberg, Lennart Swedes at War (Aberjona Press, Bedford, PA, 2010), ISBN 978-0-9777563-1-5
- Langer, Joakim Mannen som hittade Tarzan (Sivart Förlag AB, Stockholm, 2008) ISBN 91-85705-12-8.
- Arrioja, Adolfo Vizcaíno El sueco que se fue con Pancho Villa (Editorial Océano de México, 2000) ISBN 970-651-402-3
- Turner, Timothy G. Bullets, Bottles and Gardenias (Southwest Press 1937)
- Tunis, Edwin Weapons: a pictorial history P61 (The Johns Hopkins University Press 1999) ISBN 978-0-8018-6229-8