[10][11][12][13][14] Castelli had two sons, Christian, a retired Army Special Forces Colonel who was the 2022 Republican Party nominee in North Carolina's 6th congressional district, and Paul, an ordained Minister in Florida.

[18] After retiring from the State Police, he began a career as an educator, teaching at Iona College for thirteen years and rising to become Chairman of the Criminal Justice Department.

[23][24][25] Prior to his transition from public service to politics, Castelli was a regular contributor on network television including ABC, CBS, Fox News, CNN, MSNBC and Court TV.

In the 2010 general election, Castelli held the seat by defeating White Plains City Council President Thomas Roach.

[43] Winning with a slim 112 vote margin, a month-long recount was necessary before Castelli could be declared the winner, thus earning him a full two-year term representing the 89th District.

[47] His 2010 election and subsequent reelection were considered significant, as the 89th Assembly District seat to which he was elected was gerrymandered to be a Democratic district, and was home to prominent Democratic political figures, including former U.S. President Bill Clinton, Secretary of State Hillary Clinton, Governor of New York Andrew Cuomo, attorney Robert F. Kennedy, Jr. and George Soros, billionaire financier of numerous progressive causes.

[54][55][56][57] He decried the 2012 redistricting process as partisan gerrymandering, for which he was named a "Hero of Reform" by former New York City Mayor Ed Koch.

"[65] Sensing political opportunity following the redistricting process, White Plains City Councilman David Buchwald launched a challenge to Castelli, citing the district's overwhelming Democratic enrollment advantage.

[72][73][74] Yet he also held environmentalist views considered atypical for most Republican politicians, and his pro-conservation ideals garnered him support and endorsements from organizations such as the League of Conservation Voters and Sierra Club during all of his campaigns.

[75][76][77] For instance, he was a cosponsor and vocal proponent of a ban on hydraulic fracturing in the Marcellus Shale region of upstate New York, a process for natural gas exploration which is known as "hydro-fracking.

"[85][86] According to Patch Media, a regional outlet covering the 89th Assembly District, he "earned a reputation for being an independent voice in the Legislature, especially on tax policies that he says unfairly penalize Westchester County residents and business owners.

[59][91][92] In 2011, Castelli became the first member of the Minority since 2007 to pass a "statewide" bill, a veterans protection measure which prohibited public employers from abolishing positions of persons absent on military duty.

During the legislative session in 2012, Castelli authored and passed a bill to extend the statute of limitations for Vietnam Veterans to bring claims arising from exposure to Agent Orange and other phenoxy herbicides, which was signed into law by Governor Cuomo.

[102] He also authored and passed legislation to rename portions of New York State Route 120 in Chappaqua and Purchase for Staff Sergeant Kyu Hyuk Chay, and Specialist Anthony Kalladeen, soldiers from those communities who were killed in action during the wars in Afghanistan, and Iraq, respectively.