Born in Pontefract, West Yorkshire, Platt attended Easingwold School and played for Easingwold Town before joining the York City youth system in 2004.
He joined Northern Premier League Division One South club Hucknall Town on loan in October 2011, making his only appearance as a substitute against Stamford before returning to York in November.
Later in the 2011–12 season, Platt signed for Harrogate Town of the Conference North on loan on 6 March 2012, scoring on his debut later that day with Harrogate's first goal in a 6–2 home win over Corby Town.
He finished the loan with two goals in 10 appearances.
Following the end of the season he was named York's Youth Team Player of the Year, having captained the under-18 team during the season.

Platt signed a one-year professional contract with York in June 2012, following their promotion to League Two via the Conference Premier play-offs, with manager Gary Mills saying "I have high hopes for him.
He's done superbly well.
I think he's got a bright future."
He rejoined Harrogate on a three-month loan on 27 September 2012, making his second debut for the club two days later in a 2–2 draw at Worcester City.
He played in five FA Cup matches for Harrogate, including their matches against Conference Premier team Hyde in the fourth qualifying round and League Two team Torquay United in the first round.
He scored in the second round against Hastings United in a 1–1 draw, and scored a 90th-minute equaliser in the replay, although Harrogate lost 5–4 in a penalty shoot-out after a 1–1 extra-time draw.
He scored eight goals in 11 appearances before returning to York in December 2012.

Platt signed for another Conference North club, F.C. Halifax Town, on a one-month loan on 17 January 2013.
His debut came in a 5–1 win at Corby Town on 2 February 2013.
Having made three appearances for F.C. Halifax he returned to Harrogate on 22 February 2013, signing on loan for the rest of 2012–13.
Platt marked his return with Harrogate's opening goal in a 2–0 win away to Gloucester City on 23 February 2013.

He was recalled by newly appointed York manager Nigel Worthington on 21 March 2013, having scored three goals in six matches during his third spell with Harrogate.
He made his York debut in a 2–1 defeat away to Torquay on 23 March 2013, entering the match as a half-time substitute for Paddy McLaughlin.
He then started York's six remaining matches, being paired alongside Adam Reed in midfield, as York went on to avoid relegation on the final day of the 2012–13.
Platt's emergence in the team was praised by Worthington as the "biggest highlight" of York's relegation battle, and having finished his first senior season at York with seven appearances signed a new two-year contract with the club in May 2013.
Born in Pontefract, West Yorkshire, Platt attended Easingwold School and played for Easingwold Town before joining the York City youth system in 2004. He joined Northern Premier League Division One South club Hucknall Town on loan in October 2011, making his only appearance as a substitute against Stamford before returning to York in November. Later in the 2011–12 season, Platt signed for Harrogate Town of the Conference North on loan on 6 March 2012, scoring on his debut later that day with Harrogate's first goal in a 6–2 home win over Corby Town. He finished the loan with two goals in 10 appearances. Following the end of the season he was named York's Youth Team Player of the Year, having captained the under-18 team during the season.
Platt signed a one-year professional contract with York in June 2012, following their promotion to League Two via the Conference Premier play-offs, with manager Gary Mills saying "I have high hopes for him. He's done superbly well. I think he's got a bright future." He rejoined Harrogate on a three-month loan on 27 September 2012, making his second debut for the club two days later in a 2–2 draw at Worcester City. He played in five FA Cup matches for Harrogate, including their matches against Conference Premier team Hyde in the fourth qualifying round and League Two team Torquay United in the first round. He scored in the second round against Hastings United in a 1–1 draw, and scored a 90th-minute equaliser in the replay, although Harrogate lost 5–4 in a penalty shoot-out after a 1–1 extra-time draw. He scored eight goals in 11 appearances before returning to York in December 2012.
Platt signed for another Conference North club, F.C. Halifax Town, on a one-month loan on 17 January 2013. His debut came in a 5–1 win at Corby Town on 2 February 2013. Having made three appearances for F.C. Halifax he returned to Harrogate on 22 February 2013, signing on loan for the rest of 2012–13. Platt marked his return with Harrogate's opening goal in a 2–0 win away to Gloucester City on 23 February 2013.
He was recalled by newly appointed York manager Nigel Worthington on 21 March 2013, having scored three goals in six matches during his third spell with Harrogate. He made his York debut in a 2–1 defeat away to Torquay on 23 March 2013, entering the match as a half-time substitute for Paddy McLaughlin. He then started York's six remaining matches, being paired alongside Adam Reed in midfield, as York went on to avoid relegation on the final day of the 2012–13. Platt's emergence in the team was praised by Worthington as the "biggest highlight" of York's relegation battle, and having finished his first senior season at York with seven appearances signed a new two-year contract with the club in May 2013.
Tom Platt