Alexander Tanev was born in Veles, then in the Ottoman Empire. On October 17, 1880, he enlisted in the Bulgarian Land Forces. In 1883 he graduated from the fourth class of the Vasil Levski National Military University in Sofia. On August 30, 1883, he was promoted to the rank of lieutenant and enlisted in the Life Guards Squadron . During the Serbo-Bulgarian War in 1885 he was the commander of a standard platoon of the squadron and respectively an ordinary of Prince Alexander Battenberg, but later joined his squadron on the battlefield and took part in the battles at Slivnitsa, Tsaribrod and Pirot.