[10] After graduating from law school, Hammer worked for sixteen months at the Houston office of Kirkland & Ellis LLP.

[16][17][18] With the natural law scholar Hadley Arkes, Matthew Peterson, and Garrett Snedeker, Hammer co-authored in 2021 the influential manifesto "A Better Originalism," arguing for "a bolder, more robust jurisprudence rooted in the principles and practices of American constitutionalism.

[20] He hosts America on Trial with Josh Hammer, a legal podcast primarily focused on the 2024 United States presidential election.

[22][23] The Southern Poverty Law Center reported that the Newsweek opinion section under Hammer's tenure had "emerged as a hub for opinion pieces authored by radical right activists",[24] noting its elevation of conspiracy theorists such as Jack Posobiec and Dinesh D'Souza, and its publication of conspiracy theories about COVID-19.

[25] In December 2022, Hammer attended the annual gala for the New York Young Republican Club, along with noted far-right figures such as Posobiec, Steve Bannon, Marjorie Taylor Greene, and Peter Brimelow.

[20][27][28] Hammer is vocal about Jewish- and Zionist-related issues; he has debated Peter Beinart[29][30] about the Israeli–Palestinian conflict and Alan Dershowitz about the 2023 Israeli judicial reform dispute.

[33] Hammer currently sits on the boards of advisors of American Moment,[34] the New York Young Republican Club[35] and the United Jewish Gun Coalition.