He received his episcopal consecration on the following April 8 from Archbishop Riordan, with Bishops Jean-Baptiste Brondel and Lawrence Scanlan serving as co-consecrators.

[4] In response to the growing influence of the anti-Catholic American Protective Association in Los Angeles, he organized a branch of the Catholic Truth Society in 1896.

[9][10] When it came to more secular issues, Montgomery believed, "If ever the respective rights and duties of labor and capital are to be even properly defined, it must be upon the principles which religion lays down.

[4] At the time of the 1906 San Francisco earthquake, Riordan was away on travel and it was Montgomery who led the Archdiocese's immediate response to the disaster and helped extinguish a fire at St. Mary's Cathedral.

[5] A few days later, he wrote to his successor in Los Angeles, Thomas James Conaty, to say "I do not know how I have lived through [it]" and to praise the “good humor, the common interest, and forgetfulness of self that are everywhere.