The current site of Arusha was first settled in the 1830s by the agro-pastoral Arusha Maasai from the Arusha Chini community, south of Mount Kilimanjaro.^{[4]: page 112} They traded grains, honey, beer, and tobacco with the pastoral Kisongo Maasai in exchange for livestock, milk, meat, and skins. Demand for Arusha’s foodstuffs increased substantially during the 1860s when the Pangani Valley trade route was extended through Old Moshi, Arusha, and ultimately to western Kenya.  Although not yet a town, it was a regional centre with a number of urban features.

In 1994, the UN Security Council decided by its Resolution 955 of 8 November 1994 that Arusha should host the ad hoc International Criminal Tribunal for Rwanda. The establishment of the tribunal with its foreign employees has influenced the local economy of the city increasing the cost of living for residents. The tribunal has downsized due to its closure in 2014, but its legal successor, the United Nations International Residual Mechanism for Criminal Tribunals established by United Nations Security Council Resolution 1966, will continue entertaining a branch in Arusha, opening on 1 July 2012. The tribunal indicted 93 individuals and sentenced 62