Williams, with 30 tournaments behind him on the HSBC Sevens World Series, brings a wealth of experience to head coach Paul John's side with only Rhys Shellard (with 35) having played more tournaments on the international circuit.
Pontypridd's Adam Thomas will lead the side which finished seventh in the IRB World Series last season.
World Cup selection has proved a double celebration for the Davies household. Only days after Jonathan was selected for a starting berth for the British & Irish Lions side which takes on Australia tomorrow, his younger brother James has made the trip to Russia.
Alex Webber's rapid rise continues with his selection - he began last season in the SWALEC League with Ystrad Rhondda before being handed his chance by John in Dubai in the second round of last year's world series. Still only 21, he is the youngest member of the squad.
Cardiff duo Gareth Davies and Alex Walker have both returned to Sevens duty having spent time with the Cardiff Blues last season while Rhys Jones returns to the fray having recovered from an injury which kept how out of the last two legs of the world series.
Llandovery speedster Chris Knight has also been included along with Llanelli's Craig Price, Carmarthen Quins' Jason Harries and Llandovery's Adam Warren who has just returned from Wales' two Tests in Japan.
Wales Sevens World Cup squad:
Adam Thomas (Pontypridd), Alex Webber (Ystrad Rhondda), Lee Williams (Carmarthen Quins), Gareth Davies (Cardiff), Chris Knight (Llandovery), Rhys Shellard (Pontypridd), James Davies (Carmarthen Davies), Alex Walker (Cardiff), Adam Warren (Llandovery), Craig Price (Llanelli), Jason Harries (Carmarthen Quins), Rhys Jones (Llandovery).