With his trademark boaters, cricket sweaters, bow ties, color-blocked tuxedos and 24-carat-gold microphone, Cassidy is known for his work at celebrity functions, including the 50th birthday party and 2009 inauguration of President Barack Obama, and the 2008 wedding of Beyoncé and Jay-Z.
Born in New York's Upper East Side, Cassidy is the son of the music agent Jonny Podell. Interested in deejaying from an early age, Cassidy describes himself as a "hip-hop kid": "When I was three years old, I would watch cult classic dance films Breakin' and Breakin' 2: Electric Boogaloo. When I was five years old, I would jump up and down on my bed to Run DMC. When I was 13, I idolized Grandmaster Flash, [DJ] Kool Herc, and Afrika Bambaataa. DJing was my way of contributing to the culture."
For his tenth birthday, he asked his parents for two turntables and a mixer. He worked at teenage parties, school carnivals and talent shows; from his senior year at high school he started working in nightclubs. In 1999 he began his undergraduate studies at George Washington University before transferring to New York University, where he graduated in sociology in 2003.
Cassidy was discovered by Sean "Diddy" Combs while working the 10–4 night shift in the basement of Lotus, a club in Manhattan. Combs wrote his phone number on a napkin and asked Cassidy to call him, which led to invitations to work at Grammy parties and the MTV Video Music Awards.
As of 2011, according to Forbes, Cassidy was performing 200 gigs a year, sometimes earning $100,000 a night. He has worked at parties hosted by Oprah Winfrey and Anna Wintour, and at the weddings of Beyoncé, Jennifer Lopez and Kim Kardashian. After he worked at the opening party in 2009 for Oprah Winfrey's girls' school in South Africa, she recommended him to the Obamas. He worked at President Obama's first inauguration ball in 2009, the president's and Michelle Obama's 50th birthdays, and at the 2012 Democratic National Convention.
During performances, Cassidy uses two CDJ 2000 digital turntables by Pioneer Electronics, a Pioneer DJM-900, in-ear headphones custom-made by JH Audio, and a 24-carat-gold microphone custom-made by Shure. He has become known for his trademark boaters, cricket sweaters and tuxedos, often in pink and green.
Cassidy announced in 2013 that he was working on his first album, Paradise Royale, which he said aimed to "bring back the greatest and most universal dance music of all time," capturing the architecture of 1978–1982 dance music. Cassidy said he was bringing together a 14-piece string section and 22 of the world's most notable musicians from that period. The album was expected to be released in May 2014.
While working on the album, Cassidy created an iTunes playlist of 25 songs recorded between 1978 and 1982, then set about researching how to make his music sound like those songs. He realized that the producers had repeatedly used the same musicians to create the sound. Those are the musicians he sought to recruit for Paradise Royale.
The album's lead single, "Calling All Hearts", sung by Robin Thicke and Jessie J, was released in the US on iTunes in February 2014. It featured Nile Rodgers on guitar, Verdine White on bass, Philip Bailey on percussion and background vocals, Larry Dunn on keyboards, John "JR" Robinson on drums, and Jerry Hey on horns and strings. The video, with a 13-piece band performing on a pink heart-shaped stage, was directed by Director X and shot in London.
Director X also directed the video for the second single from the album, "Make the World Go Round", which was shot on an elevated train in Chicago. Featuring R. Kelly, the single was released in the US in April 2014. On "Calling All Hearts", Nile Rodgers played the same guitar as on Chic's "Good Times" and Sister Sledge's "We Are Family". On "Make the World Go Round", Ndugu Chancler used the same drums as on Michael Jackson's "Billie Jean".