He serves in the New York State Assembly representing the 40th District, which includes portions of Whitestone, Flushing, College Point, and Murray Hill in Queens.

In 2006, Kim joined the staff of then-New York City Council Speaker Christine Quinn as a Policy Analyst, where he focused on legislative issues relating to transportation, infrastructure, and economic development.

[12] After leaving his position at the Governor’s office, Kim worked at the Parkside Group[13] where he advocated on behalf of children with special needs, small business, community organizations, and vulnerable New Yorkers.

[16] Running on a plan to end corporate welfare in what The Villager described as "one of the most jam-packed elections in recent memory," he and over a dozen other candidates entered a crowded race eventually won by then-Councilmember Jumaane Williams.

[20] During the 2024 New York Democratic presidential primary, Kim stated that "[t]here were clear patterns of foreign influence trying to dictate the outcome of the election — groups with ties to mainland China and the CCP.

[22] In his first month in office, Kim helped pass legislation (A.3354) which implemented tax relief for New York City homeowners; the bill was projected to encourage housing development.

Kim has sponsored legislation inspired by events that happen in his district; in January 2013, he became a proponent of the Taxi Drivers Protection Act following a robbery and assault that occurred in Brooklyn.

[29] In October 2018, he organized more than 20 labor groups, nonprofits and community leaders to call for a one-time cancellation of student debt and outlined the economic rationale and financial mechanisms for how it could be executed.

[41] He subsequently introduced and became the primary sponsor of a bill to relieve the financial and economic burdens that small business owners, including those in the nail salon industry, were facing.

[47][48][49][50] Richard Bernstein, a former New York Times reporter, expressed serious doubts about its claims of widespread abuses and "astonishingly low" wages, and showed that its translation and understanding of job ads in the industry, one of its key pieces of evidence, were either inaccurate or false.

[47] In October 2015, Reason published a three part re-reporting of the story by Jim Epstein, charging that the New York Times' series was filled with misquotes and factual errors with respect to both its claims of illegally low wages and of health hazards.

[55] Subsequently, Kim stated that he believed the suspect was suffering from a mental health problem, and expressed hope that the individual was not simply punished but also given the help and treatment he needed.

Kim said that the incident, and the efforts to understand how the would-be mugger ended up in that situation, gave him more insight into the importance of effective policies to address homelessness, mental health problems, and other long-term issues.