Born near Ville Platte, Evangeline (then St. Landry) Parish, Louisiana. He was the son of Marie Denise Ortego, a daughter of one of Ville Platte’s founding Hispanic families, and Alexandre Lazaro, an immigrant from the town of Risan in what is now Montenegro in the Balkans. Lazaro attended public and private schools and Holy Cross College, New Orleans, Louisiana. He was graduated from Louisville (Kentucky) Medical College in 1894 and practiced his profession in Washington, Louisiana, until 1913.
He became interested in agricultural pursuits. He served as president of the parish school board for four years. He also served in the Louisiana State Senate from 1908 to 1912.
Lazaro was elected as a Democrat to the Sixty-third and to the seven succeeding Congresses and served from March 4, 1913, until his death in Washington, D.C., March 30, 1927. He became the second Hispanic American ever to chair a standing committee in the U.S. House of Representatives when he was named chairman of the Enrolled Bills Committee in 1915. He was interred in the Old City Cemetery, Ville Platte, Louisiana.