[1][2] Hornstein was born in Cincinnati, Ohio, in 1959 to parents of Hungarian and Polish descent who survived the Holocaust in Germany.

[4] He was appointed to the Twin Cities Metropolitan Council by Governor Jesse Ventura in 2000, serving until his election to the legislature.

[20][21] He has pushed for stricter speed limits on city streets to protect pedestrians and bicyclers, increasing the use of electric buses, and reducing the number of drivers on roads.

[28][29] He also authored bills to make it illegal to use a cellphone while driving without a hands-free device, which faced opposition from House Republicans.

[32] The bill was reintroduced under DFL control, passed the House with bipartisan support, and was signed by Governor Tim Walz in April 2018.

[33][34][35][36] Hornstein has advocated for greater regulation of railroads, especially oil trains, and authored amendments and bills requiring companies to share the cost of rail line upgrades.

[41][42][43] He has supported guidance from the National Transportation Safety Board that recommends hazardous oil cargo be routed away from population centers, and criticized the Trump administration for rolling back regulations.

[49] He has supported increasing bus-rapid-transit projects, including the Orange Line, which would run from downtown Minneapolis to Burnsville.

[53][54][55] He has criticized the council for lacking transparency, public input, and adequate environmental reviews, for cost overruns,[56][57] and for its handling of the Southwest Light Rail project; he supported audits of the council's performance and legislation to transfer the project to the Minnesota Department of Transportation.

In 2009, he led a bipartisan delegation to Israel, and traveled to Germany to explore green energy and jobs policy.

[67][68][69] Hornstein has spoken out against increasing hate crimes against Jewish, Muslim, Asian, and LGBTQ Americans, and authored legislation that would require the Attorney General's office to review hate-crime laws.