Best, who has recovered from an ankle skin infection, has not featured since the game against Dragons at the start of December.
Abbey Insurance Academy scrumhalf Johnny Stewart has earned a first senior start for the Province, having made his debut off the bench against the same opposition earlier in the season.
Best will start at hooker and will be joined in the front row by Callum Black and Rodney Ah You. Pete Browne will play for the first time since September after being named in the second row alongside Iain Henderson.
Matty Rea, Sean Reidy and Jean Deysel will combine in the back row.
Stewart will be partnered at half back by Christian Lealiifano, while Stuart McCloskey and Darren Cave, who scored a try and made an assist in Monday’s win versus Munster, are retained in midfield.
Ireland international wingers Andrew Trimble and Jacob Stockdale are joined in the back three by All Black fullback Charles Piutau.
Rob Herring, Kyle McCall and Wiehahn Herbst are the front row replacements, with Alan O’Connor and Nick Timoney providing additional forward cover. John Cooney, Johnny McPhillips and Tommy Bowe are the backline options on the bench.
There will be live TV coverage on Sky Sports and BBC2 NI.
Ulster Rugby team to play Leinster, Guinness PRO14, Saturday 6th January, RDS Arena, kick-off 5.35pm:
(15-9): C Piutau; A Trimble, D Cave, S McCloskey, J Stockdale; C Lealiifano, J Stewart;
(1-8): C Black, R Best (captain), R Ah You, P Browne, I Henderson, M Rea, S Reidy, J Deysel;
Replacements (16-23): R Herring, K McCall, W Herbst, A O’Connor, N Timoney, J Cooney, J McPhillips, T Bowe.
Unavailable due to injury/illness:
Marcell Coetzee, Matthew Dalton, Robbie Diack, Craig Gilroy, Chris Henry, Brett Herron, Rob Lyttle, Luke Marshall, Paul Marshall, Adam McMurney, Jared Payne, Johnny Simpson, Kieran Treadwell.