Born in
Florence,
Tuscany, Tonelli started his professional career at
Empoli. He made his debut during the
2010–11 Serie B season, marking his first appearance on 5 September 2010. On 26 April 2015, Tonelli was punched by
Atalanta's
Germán Denis after he burst into the Empoli dressing room. Denis was subsequently given a five-match ban for this action against Tonelli. Tonelli enjoyed his breakthrough in the 2014–15 season under then manager
Maurizio Sarri, attracting the attention of some of the top Italian teams. On 23 May 2016, it was announced that Tonelli had signed for
Napoli. The transfer fee was reported as being €10 million. On 7 January 2017, Tonelli made his Napoli debut, scoring the match-winning goal in the 95th minute of a 2–1 home win over
Sampdoria. On 17 August 2018, Tonelli joined
Serie A side Sampdoria on loan until 30 June 2019. On 23 January 2020, he joined
Sampdoria on another loan until the end of the 2019–20 season, at the end of which Sampdoria will have an obligation to purchase his rights permanently. He also signed a contract with Sampdoria until 30 June 2022. On 27 August 2021, Tonelli return to
Empoli after 5 years. ==International career==