[1] Walsh was ordained to the priesthood for the Diocese of Buffalo by Bishop James Edward Quigley on January 27, 1900.

[citation needed] On May 10, 1918, Walsh was appointed bishop of the Diocese of Trenton by Pope Benedict XV.

He received his episcopal consecration on July 25, 1918, from Archbishop Giovanni Bonzano, with Bishops Dennis Dougherty and John O'Connor serving as co-consecrators.

[1] Walsh was among those, who with Christian Brother Barnabas McDonald encouraged the Knights of Columbus to consider working with youth.

To this end, in August 1922, Walsh addressed the annual meeting of the Supreme Council of the Knights of Columbus held in Atlantic City.

[5] In 1910, five sisters of the Religious Teachers Filippini were sent by Pope Pius X to work among the Italian immigrants in St. Joachim's parish in South Trenton.

Walsh became a supporter of their work, and in 1918, with the help of a donation from businessman James Cox Brady, he acquired the Harvey Fisk estate "Riverside" in Ewing Township for the sisters.

In 1933, the sisters established Villa Victoria Academy, an all-girls, private, Catholic middle and high school.

[11] Upon the elevation of the Diocese of Newark to the rank of archdiocese by Pope Pius XI, Walsh was appointed its first archbishop on December 10, 1937.