Born in
Bridgend, Wales, and later
Cwmtawe Community School in
Pontardawe while playing for the
Swansea City Academy. Jefferies made 14 appearances for the Swansea under-18 team during the 2016–17 season. He appeared on trial for
Colchester United's under-18 and
under-23s in early 2017. Colchester confirmed the signing of Jefferies from Swansea on 28 July 2017. On 31 January 2018, he left Colchester and signed for
Scottish Premiership side
Dundee after appearing for the club on trial. He made his senior debut on 5 May 2018, against
Hamilton Academical. At the end of the
2018–19 season, Jefferies was released by Dundee. ==International career==