Brucella melitensis is primarily a cause of abortions in sheep and goats. It can be isolated from cattle, water buffalo, and camels, and transmits to humans through unpasteurized milk and cheeses. Little was known about the distribution of this organism around Iraq, which was needed for developing an effective control campaign. The goals of this study, initiated in 2005 in collaboration with the Food and Agriculture Organization (FAO), were to determine the prevalence of Brucella in sheep, goats, cattle, water buffalo, and camels across Iraq, and to test the effectiveness of a whole cell vaccine. Villages for sampling were selected from 15 governorates that had more than 2000 animals. In each governorate, goats and sheep were sampled in 17 villages, cattle and water buffalo in 11 villages, and camels in 9 villages; 60 animals were sampled in each category per village. Serum samples initially screened by the Rose Bengal test were further confirmed by ELISA. These results indicated that 6.5% (6.1–6.9, 95% CI), 1.0% (0.78–1.2, 95% CI) and 1.5% (1.2–1.8, 95% CI) of sheep and goats, cattle, and water buffalo were positive for B. melitensis, respectively. Prevalence for sheep and goats ranged from 0.2% in Murhana to 16.4% in Kirkuk, for cattle from 0.02% in Thyqar to 11.1% in Muthana, and for water buffalo from 0% in Babylon to 5.4% in Basrah. Approximately 1 to 2 × 10⁹ cfu of the live attenuated B. melitensis vaccine, Rev1, was used to vaccinate 1.8 to 2.5 million lambs and kids each year, across all 15 governorates, from 2009 to 2014. During this time, cases of abortion in sheep and goats fell from 5090 in 2011, to 322 in 2013. This study concluded that the incidence of Brucella varies across different regions of Iraq, which can be related to animal handling practices. An aggressive strategy of vaccination was effective in reducing abortions in sheep and goats by over 90%. During the course of the vaccine intervention in this study, the Iraqi Ministry of Health reported that the incidence of brucellosis in humans decreased from 24 to 7 incidences per 100,000 people, further indicating an effective vaccination program.