Simcha Eichenstein was born to a rabbi from a prominent Bobover rabbinical family in Borough Park, Brooklyn, where he grew up and attended yeshivas.

[7][8] On April 26, 2018, Eichenstein announced his candidacy for the open New York State Assembly District 48 seat, covering most of Borough Park and part of Midwood, Brooklyn, being vacated by Dov Hikind.

As Hikind's hand-picked successor,[9] Eichenstein was considered to be the front-runner in the race, running unopposed as the Democratic candidate in the primary election in September 2018.

"[15] In October 2020, during the COVID-19 pandemic, Eichenstein said he was "outraged" with the "draconian measures" implemented by Governor Andrew Cuomo to curb the spread of coronavirus in various neighborhoods of New York City.

[16][17] Assembly Speaker Carl Heastie appointed Eichenstein to serve on a number of committees, including Aging, Cities, Housing, Real Property Taxation, and Social Services.