Hughes has prior experience of driving Formula E machinery, having completed two tests for the NIO 333 team and a third one with Mercedes in Marrakesh last year.
The British driver has been racing at F3 level since 2016 and has racked up six victories during that period with DAMS, ART and HWA.
The 26-year-old also made his Formula 2 debut last year with HWA, replacing Giuliano Alesi at Sochi following the French driver’s mid-season move to MP Motorsport.
In his new role with Mercedes’ customer team Venturi, Hughes will work alongside the team all season and will remain on hand to deputise for race drivers Norman Nato or Edoardo Mortara if required.
”I’m incredibly excited to join ROKiT Venturi Racing as the team’s reserve driver,” said Hughes. “I want to say a big thank you to Susie [Wolff] and the team for trusting me with this opportunity.
“I’ve driven Formula E cars in the past, most recently with Mercedes, so I feel ready to do my job.
“I’m looking forward to supporting Edo and Norman this season and I’m excited to help the team make the car as fast as possible while, of course, learning on the way. Formula E is an incredibly exciting championship, and it feels fantastic to be back at a race track.”
Venturi announced in December that it has been sold to an investor group led by Formula E’s co-founder Alejandro Agag, but Susie Wolff has remained as the team principal following the change of ownership.
Wolff said: ”The role of the reserve driver is crucial in Formula E especially during these challenging times with the global pandemic.
“Jake has done more than prove his talent and natural ability on the junior single-seater ladder and we’re delighted to welcome him to ROKiT Venturi Racing.”