A member of the South West Africa People's Organization (SWAPO), Simunja was appointed to the National Assembly of Namibia in 2000 and served as Deputy Minister of Defense from 2000 to 2009.

Simunja rose to the rank of lieutenant colonel in the Namibian Defence Force prior to entering political office.

Born at Linyanti in Zambezi Region, Simunja began his military career in 1975 at the age of 17, fleeing into exile in Zambia.

Simunja rose the ranks of the People's Liberation Army of Namibia, the military wing of SWAPO during the Namibian War of Independence.

Simunja came to even greater international prominence in January 2000 when he displayed 81 suspected UNITA rebels to the media at Rundu.