Saint Joshua was a "precongregation" saint, according to Wikipedia. This means there was no system for canonization at the time he lived and served as a disciple of God and a follower of Moses.
According to the Official King James Online, Joshua is known for leading the Israelites into the promised land. Saint Joshua is recognized as a saint by virtue of having received a direct order from God by way of Moses and acting as the leader of the Israelites in their travels and in battle. Known as a saint for his works and not by canonization, his role as patron saint is interpreted differently among followers.