From a very early age, Jefferson dedicated himself to pursuing a career in the performing arts. In 1999, he joined his local Stagecoach Theatre Arts School, in Plymouth, Devon, and played a diverse range of roles in productions such as Bugsy Malone to devised plays. This led him to become an avid improviser, facilitating his own improvisation group during his professional training. 

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He moved to Guildford in 2012 to develop his craft further at the Performance Preparation Academy, before continuing to study Musical Theatre at the London College of Music, with the University of West London, where he achieved a BA (Hons).

​​Upon achieving his degree in 2015, Jefferson made his professional debut in the role of Merlin in the UK TiE (Theatre in Education) Tour of The Sword in the Stone with Image Musical Theatre. Immediately following his highly successful run of 162 performances to schools around the UK, Ireland, Scotland and Wales, he delighted international audiences as Lead Male Vocalist in a series of digitally-enhanced production shows with entertainment provider Live Business and TUI Group. His work in this role earned him the Excellent Customer Service Award, which 'recognised and appreciated hard work and dedication', and was presented to him at the TUI Awards Ceremony 2016 in Rhodes, Greece. ​

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Later that same year, Jefferson reunited with Live Business as the Entertainment Host and Vocalist at TUI Gold's Yaramar Hotel in the Costa del Sol, Fuengirola, where he had a particularly noteworthy 6-month residency, performing and presenting first-class entertainment. He was invited back as Resident Vocalist in early 2020 to perform his solo concert An Evening with Jefferson Parlett for a 2-month run. 

From September 2018 to March 2019, Jefferson took to the high seas as the role of Entertainment Host and Vocalist, onboard the Pacific Aria with P&O Australia Cruises. He delivered exceptional, world-class entertainment to live audiences across the pond, before setting sail again for the remainder of the year with Brittany Ferries as the Cruise Entertainment Manager and Vocalist onboard their fleet.  

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In October 2021, he toured around the UK with Troubadour (Male Vocal Harmony Group) - performing their globally successful show of acapella and classic songs, reimagined in stunning four part harmony, in some of the country's biggest holiday resorts. 

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His career took to new levels between 2022 and 2023. He starred in the short film I Know Something Happened, directed, produced and written by Cutting It (BBC) and Emmerdale (ITV) star Sian Reeves, which led the actress into winning the Special Jury Award in Direction at the first season of the Casablanca Film Factory Awards. 2023 also saw Jefferson making his television debut playing the younger incarnation of Mark Williams’ titular role in BBC's crime drama Father Brown. Shortly after, he was cast as a dancer in a TV commercial for UK holiday resort Butlins' Adult Weekenders before appearing as Buttons (and serving as Sound Designer and Vocal Captain) in Rugeley Rose Theatre's production of Cinderella, written and directed by Richard Cheshire, in Staffordshire. 

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Jefferson has recently completed filming for BritBox's crime drama spin-off Sister Boniface Mysteries, playing the role of Floor Manager in the show's forthcoming second season - as well as guest roles in two episodes of BBC's long-running medical drama Doctors.

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Coinciding with his career, Jefferson is currently at Staffordshire University, having won a place on the world’s first year-long MA in Contemporary Pantomime Practice. 

As a presenter, he produced and co-presented his self-penned radio show The Jeff Parlett and Benny Bright Show on Blast Radio, broadcasting from the legendary Ealing Studios from 2012 to 2015. Between 2020 and 2021, Jefferson served both as a Presenter and Music Researcher for the music-based game shows Rock and Roll Bingo, Bingo Beats and Bonkers Bingo with entertainment providers Live Business, and Scarlett Entertainment, for the UK’s largest chain of bingo clubs, Mecca Bingo.