He attended St Mary's Menston Catholic Voluntary Academy and, later, joined Huddersfield's Town Academy in the late 2000s, eventually becoming the captain of the under-18 team in 2012. During the same year, Sinnott was offered a professional contract. Following the sacking of Simon Grayson as Huddersfield manager on 24 January 2013, the manager of the under-18 team, Mark Lillis, was promoted to the role of caretaker manager, and gave Sinnott his first appearance in the Huddersfield first team in their 1–1 draw against Leicester City in the 4th round of the FA Cup at the John Smith's Stadium on 26 January 2013. After the match, Sinnott expressed being positive on his debut and described himself as "not really the nervous type!" His first league appearance was as a substitute in Town's 6–1 defeat by Nottingham Forest at the City Ground on 19 February 2013. Despite only making two appearances, Sinnott was offered a new two-year contract by the club, which he signed, keeping him at the club until 2015. After eight years at the club, Sinnott was released by Huddersfield after having his contract terminated by mutual consent on 2 February 2015, with his contract due to expire in the summer.
Loan spells
After being told by Huddersfield Town's management that he would be loaned out, it was announced on 6 December 2012, he joined his father, Lee, at Conference North side Altrincham for a month, making six appearances before returning in January 2013. On 7 August 2013, Sinnott joined Bury on a six-month loan from Huddersfield Town. Sinnott then made his Bury debut three days later, coming on as a substitute for John Rooney in the second half, in a 2–1 loss against Oxford United. Sinnott then scored his first goal in the next game, as Bury beat Accrington Stanley 3–0. After making 10 appearances for the Shakers, he was recalled by Huddersfield on 18 October.
Later career
After being released by Huddersfield Town, Sinnott rejoined his father at Conference North side Altrincham for the second time. He then had spells at F.C. Halifax Town and Chesterfield before joining Alfreton Town in 2018; at the time of his death he was playing for Matlock Town.
Death
Sinnott was found unconscious with a suspected fractured skull in Retford, Nottinghamshire, in the early hours of 25 January 2020, following an altercation in which he was attacked and sustained a head injury. He was admitted to the Northern General Hospital in Sheffield in a critical condition where he died just before 19:00 that evening. Matlock Town and his former club Alfreton Town had both postponed their respective matches earlier that day. Police arrested a 21-year-old man and a 27-year-old man in connection with the fight. He carried a donor card at the time of his death. In a tribute to his death, his brother Tom as well as his dear friend Duane Holmes sent an appeal to football clubs across the country to send in shirts with Sinnott's name on the back for his funeral. 800 different football shirts were donated from around the world, these were displayed at his funeral at Bradford City's stadium. It was announced that after the funeral, the football shirts would be donated to Sport Relief.
