Voyce, 31, began his career at Bath, where he made the first of his nine England appearances, which included three tries. He joined Wasps in 2003 and over the next seven seasons won two Heineken Cups in 2004 and 2007 and three Premiership titles in 2004, 2005 and 2008.
He moved to Gloucester in 2009 and helped the club to LV=Cup success in 2011, setting the Cherry and Whites on their way to a 34-7 win over Newcastle with an early try.
"I am delighted to be joining London Welsh and excited to be able to contribute to what has been a good start to their season. Lyn and the players have been great in welcoming me into their culture," said Voyce.
"For me it's a case of getting my head down and proving a few points. There are some great challenges ahead for us as a team and that is what rugby is all about."
Voyce is one of 12 changes made by Jones to the side that provided the club with its first-ever victory in Europe, a 32-31 win over l Cavalieri Prato. Second row Martin Purdy, who won Heineken Cup and Premiership medals during a seven-year career at Wasps, flanker Michael Hills and Seb Jewell, another former Wasp, are the only survivors from that team.
Sonny Parker returns to the Welsh starting line up from the injury in suffered in the Exiles' defeat to Gloucester at the Kassam Stadium on September 30.
London Welsh: 15. Tom Voyce*, 14. Phil MacKenzie*, 13. Sonny Parker*, 12. Seb Jewell, 11. Nick Scott, 10. Gavin Henson*, 9. Tyson Keats, 1. Franck Montanella*, 2. Neil Briggs, 3. Paulica Ion*, 4. Martin Purdy , 5. Matt Corker, 6. Jonathan Mills (capt), 7. Michael Hills, 8. Ed Jackson.
Replacements: 16. Dan George, 17. Tom Bristow, 18. Arthur Joly, 19. Kirill Kulemin*, Alfie To'oala*, 21. Nick Runciman, 22. James Lewis, 23. Joe Ajuwa.
* Denotes full international