The Department of Territories [I] was established on 11 May 1951 by Executive Council Meeting No 23 (Prime Minister's Minute No 50) taking most of its functions from the Department of External Territories [I].  It also took over the administration of Ashmore and Cartier Islands and of the Northern Territory from the Department of the Interior [II].  The functions of the newly established Department as listed in the Administrative Arrangements Order published in the Commonwealth of Australia Gazette No 46 of 2 July 1951 were:
 
 Administration of Territories, viz:
  Ashmore and Cartier Islands
  Nauru
  New Guinea
  Norfolk Island
  Northern Territory
  Papua
 Australian New Guinea Production Control Board
 Australian School of Pacific Administration
 British Phosphate Commissioners
 Christmas Island Phosphate Commission
 Expropriated Properties (New Guinea)
 Shipping Services to certain Pacific Islands
 Shipping services within the Territories of Papua and New Guinea  
 Transfer of prisoners from the External Territories
  and the Northern Territory
 
The Acts to be administered by the Department of the Territories [I] were listed in the same order as being:
 
 Ashmore and Cartier Islands Acceptance Act 1933
 Christmas Island Agreement Act 1949
 Nauru Island Agreement Act 1919
 Nauru Island Agreement Act 1932
 Norfolk Island Act 1913
 Northern Territory Acceptance Act 1910
 Northern Territory (Administration) Act 1910
 Northern Territory Representation Act 1922
 Papua and New Guinea Act 1949
 Removal of Prisoners (Territories) Act 1923
 Treaty of Peace (Germany) Act 1919 (Section 2 and Part II, Treaty of
  Peace Regulations).
 
In 1955 the Department of Territories [I], assumed the administration of the Cocos (Keeling) Islands when these were transferred from the Colony of Singapore and placed under the authority of the Commonwealth by the Cocos (Keeling) Islands Act 1955. Similarly in 1958 the Department assumed the administration of Christmas Island (which was previously a separate colony administered by the United Kingdom) by the authority of the Christmas Island Act 1958.
 
On 28 February 1968 the Department of Territories [I] was abolished by Executive Council Meeting No. 9 (Prime Minister's Minute No. 4) and all of its functions (except the administration of Ashmore and Cartier Islands and of the Northern Territory, which was assumed by the Department of Interior [II] (CA 31) were transferred to the newly created Department of External Territories [II] (CA 1284).
 
The following were Ministers for Territories:

11 May 1951 - 18 Dec 1963  : Hon Paul Meernaa Caedwalla Hasluck 
                             (CP 115) 
18 Dec 1963 - 28 Feb 1968  : Hon Charles Edward Barnes (CP 64)
 
The Secretaries to the Department of Territories [I] were:
 
11 May 1951 -    May 1964  : C R Lambert, CBE
16 May 1964 - 27 Feb 1968  : G H Warwick Smith, CBE (CP 319)  

Historical agency address
  1951-by1962: Commonwealth Offices, Barton, Canberra, ACT
by1962-  1968: Derwent House, Hobart Place, Canberra City, ACT
Legislation administered
Creation: Executive Council Meeting No. 23 (Prime Minister's Minute No. 50) of 11 May 1951
Abolition: Executive Council Meeting No. 9 (Prime Minister's Minute No. 4) of 28 February 1968

Previous agency unregistered

1955: Agency within CO 40, Colony of Singapore, responsible for Cocos
      (Keeling) Islands 
1958: United Kingdom, Colonial Office (For Christmas Island)