[8] He was called to Pest, Hungary, in 1851, where his views met with such opposition that the Emperor of Austria ordered his temple closed only two months after his arrival.

[4] Einhorn emigrated to the United States and was named on September 29, 1855, as the first rabbi of the Har Sinai Congregation in Baltimore.

In that role, Einhorn formulated the Olat Tamid siddur for use in services, which became one of the models for the Union Prayer Book published in 1894 by the Central Conference of American Rabbis.

[10] Einhorn remained an opponent of interfaith marriage, arguing in Sinai that such practices were "a nail in the coffin of the small Jewish race", though he opposed the retention of practices such as the wearing of phylacteries, the limitations on activity prohibited on the Sabbath, and kosher dietary laws, all of which he viewed as outmoded.

[11] In 1861, Einhorn rebutted a sermon by rabbi Morris Jacob Raphall that supported the existence of slavery.

Einhorn retained the position as spiritual leader of the merged synagogue, delivering his final sermon on July 12, 1879, after which the congregation agreed to bestow upon him a pension of $3,500 (~$114,450 in 2023).

[4] Upon his retirement, Einhorn was recognized across denominations by his fellow rabbis; at a farewell ceremony held at his apartment (at his request, because of his health[13]) he was presented with a resolution adopted at the convention of the Union of American Hebrew Congregations, that recognized Einhorn for his rabbinic service, noting the "ability and character which have marked his career, and the earnestness, honesty and zeal which have animated the heart of a man whom we proudly recognize as one of Israel's purest champions and noblest teachers.

[4] His funeral was held before a packed house at Beth-El on November 6, 1879, where his plain coffin was carried into the synagogue by 12 pallbearers and placed before the pulpit.

Attending were such rabbinic notables as Richard James Horatio Gottheil of Congregation Emanu-El, Einhorn's son-in-law and successor Kaufmann Kohler of Beth-El, another son-in-law, Emil G. Hirsch, of Louisville, Kentucky, along with representatives of the congregations he served in Baltimore and Philadelphia.