She served as general counsel for the Service Employees International Union (SEIU) from 2017 to 2024 and a partner at the law firm of James & Hoffman.

In 1990 in Tel Aviv, she founded the Bat Adam organization, an advocacy group for victims of sexual assault and domestic violence.

[7][9][10][11] The subsequent legal case, Berner-Kadish v. Minister of Interior, challenged the refusal to register Kadish and Berner's second parent adoption of their son.

The Israel Supreme Court ruled that the Ministry of Interior must register the adoption decree, accepting legally that the child has two mothers.

[7][12][13] From 1996 to 1997, Berner worked as a clerk for Judge Betty Binns Fletcher of the United States Court of Appeals for the Ninth Circuit, and from 1997 to 1998, she worked as a law clerk for Chief Judge Thelton Henderson of the United States District Court for the Northern District of California.

[14][16] Her work with the SEIU has included legal efforts to support the Affordable Care Act, to oppose the Defense of Marriage Act, and to oppose an effort to end the Deferred Action for Childhood Arrivals (DACA) program during the Trump administration.

[8] In 2019, liberal group Demand Justice included Berner on their list of suggested Supreme Court nominees for any future Democratic president.

President Biden nominated Berner to the seat vacated by Judge Diana Gribbon Motz, who assumed senior status on September 30, 2022.