Joe joined the Northampton Town academy in November 2009. He made his senior debut for the club as a 75th-minute substitute replacing fellow countryman Alex Revell in a 1–1 draw with West Ham United U23s in the EFL Trophy on 8 November 2016.
On 13 December, he was handed an FA Cup debut (in Northampton’s 1–0 away defeat to Stourbridge). Iaciofano entered the field in the 91st-minute, coming on in place of Jak McCourt. He also came on in stoppage time to make his senior league debut in a 0–1 defeat away to Sheffield United on 31 December 2016.
After returning from his work experience loan at neighbouring Corby Town; Iaciofano signed a professional contract with Northampton Town in the summer of 2017.
On 6 May 2019, Iaciofano was told by Northampton that they would not be extending his contract.