Squadron served as a consultant to New York City's Department of Education and worked as a staffer on Congressman Anthony Weiner's 2005 mayoral campaign. He served as an aide to U.S. Senator Charles Schumer, helping the New York senator with his book .''
State Senate
Squadron ran for the 25th district of the New York State Senate in 2008. He received the endorsements of Schumer, Congressman Anthony Weiner, Manhattan Borough PresidentScott Stringer, and Mayor Michael Bloomberg. Assisted by family friends, Schumer supporters, and an aggressive campaign strategy, Squadron defeated incumbent state senator Martin Connor and took 54% of the vote. On November 6, 2012, Squadron was elected to the state senate again, this time to represent the 26th district. He beat his Republican opponent, J. Haro, 86% to 14%. Squadron won reelection in 2014 in a landslide over Republican candidate Wave Chan; and he ran unopposed in 2016, running on both the Democratic and Working Families Party lines. Squadron's platform included opposition to luxury development in Brooklyn Bridge Park. He negotiated a deal that reduced and delayed housing in the park, and has been credited with returning $11 million in capital funding that had been cut from the park's budget. Squadron also secured millions for a waterfront park project on the Lower East Side at Pier 42, along with Schumer, and also helped secure the future of Governors Island. Squadron's proposal to link New York's wealthiest parks conservancies with under-resourced neighborhood parks resulted in hundreds of millions in new funding for community parks. In 2010, Squadron sponsored the law that brought billions in federal dollars to New York City's public housing. Squadron also passed legislation expanding middle class eligibility for the Mitchell-Lama Housing Program. Squadron's tenure included a noted focus on ethics and campaign finance reform. He passed the law prohibiting public officers from using government resources for their own for-profit business. Squadron also unsuccessfully pushed to close the "LLC Loophole," which allows nearly unlimited, often anonymous campaign contributions to flood the political process. On August 9, 2017, Squadron announced his resignation from the Senate in an opinion piece published in the Daily News. He cited "heavily invested special interests" and "cynical political deals," adding: "And the status quo has proven extraordinarily durable: It barely shuddered when the leaders of both legislative chambers were convicted of corruption."
In August 2017, Squadron announced he would be working with entrepreneur Adam Pritzker and Jeffrey Sachs of Columbia University on a national initiative focused on "stronger candidates, a sharpened approach and better policies at the state level," emphasizing "policies focused on creating a better, healthier, fairer future." In October 2017, that initiative was launched as .