[1][3] Briefly assigned to teach history at St. Francis College, Loretto,[3] Lambing spent the next forty years of Pittsburgh's post-Civil War years ministering to thousands of Catholic immigrants from Europe during both an industrial and a population boom, and was credited with calming strikers who were intent on destroying a freight depot of the Pennsylvania Railroad in the city's rail yards during the Great Railroad Strike of 1877.
Among the first academically trained historians of Western Pennsylvania, Lambing was also the first to document the beginnings of the Catholic Church in the region.
Two of his most important contributions were the first English translation, from the French, of the 1749 journal of Pierre Joseph Céloron de Blainville and the publication of the register of baptisms at Fort Duquesne.
Lambing died on Christmas Eve in 1918, and was buried in the priest's section of St. Mary Cemetery in the city's Lawrenceville neighborhood.
A lecture series, the Andrew Arnold Lambing Lectureship, was established in his honor in 1955 by the Catholic Historical Society of Western Pennsylvania.