	During World War I Matuszewski was one of the executors of Piłsudski's concept in the Russian Empire. From December 1914, he served in the Russian Army, among others as commander of an intelligence troop. After the February Revolution in 1917, he organized the Assembly of Free Poles in Saint Petersburg and participated in the formation of the Polish Corps in Russia. In December 1917 he joined the Polish I Corps in Russia under the command of General Józef Dowbor-Muśnicki.