At a young age he was inspired by Giuseppe Garibaldi and attempted to join the Redshirts in the Expedition of the Thousand for the unification of Italy in 1860 escaping to Palermo at the age of 13, but without success. A relative recognised the young boy and brought him back home. Two years later, in 1862, when Garibaldi passed by Castrogiovanni in his Expedition against Rome, Colajanni joined the troops. He reached the Aspromonte, where he was captured by government troops and deported to the island of Palmaria. Liberated after an amnesty he returned to Sicily but volunteered again with Garibaldi's troops in the Third Italian War of Independence in 1866 and participated in the Battle of Bezzecca in Trentino, northern Italy, in July 1866.