Susanto's maiden posting overseas was at the embassy in Addis Ababa, Ethiopia, where he was in charge of information affairs between 1979 and 1983. During Indonesia's 1982 election, Susanto was part of the embassy's overseas election committee.[3] He then consecutively served as the chief of economics at the permanent mission to UN bodies in Geneva (1986–1991) and at the permanent mission in New York (1993–1995) before being recalled to serve as the chief of economics cooperation bureau within Indonesia's ASEAN national secretariat. In 1999, he returned to Geneva for his appointed as the deputy permanent representative in the mission.[1][2]
Susanto was sworn in as ambassador to New Zealand on 21 May 2001[4] and presented his credentials to Governor-General Silvia Cartwright on 5 July 2001.[5] During his tenure, president Abdurrahman Wahid visited the country a week after Susanto's own arrival in June. Susanto projected a normalization of diplomatic relations, as he ensured issues barring the relations was gone, and aimed to increase the volume of business from New Zealand in Indonesia as well as people-to-people exchanges.[6] He also oversaw the opening of Indonesia's embassy in Fiji.[7] Although his term was supposed to end in 2004, in 2002 he was recalled to Jakarta in light of organizational restructuring within the foreign ministry.[8] He was appointed to lead the newly established directorate general of multilateral economic, financial, and development affairs and was sworn in on 3 May 2002.[2][9][10][11] He played a key role as Indonesia's chief negotiator during the World Trade Organization Ministerial Conference of 2003.[12]
On 29 March 2005, Susanto was installed as Indonesia's ambassador to Italy, with concurrent accreditation to Cyprus, Malta, the Food and Agriculture Organization, World Food Programme, and the International Fund for Agricultural Development.[13] Susanto presented his credentials to president Carlo Azeglio Ciampi of Italy on 28 June 2005,[14] Director General of the Food and Agriculture Organization Jacques Diouf on 20 July 2005,[15] president Tassos Papadopoulos of Cyprus on 30 September 2005,[16] and president Eddie Fenech Adami of Malta on 27 October 2005.[17] As ambassador, Susanto was an ex-officio alternate governor of the International Fund for Agricultural Development.[18] Susanto departed his post in October 2008 and was replaced by his deputy chief of mission, Yuwono Agus Putranto, who acted as chargé d'affaires ad interim. In December 2009, Susanto became the senior adviser to coordinating minister for people's welfare Agung Laksono for international relations.[19] At the end of his term, Susanto received an award from the coordinating ministry as a principal associate.[20]