D'Arcy is now the most capped Leinster player of all-time having overtaken Shane Horgan in his last game against Connacht three weeks ago.
He will also incidentally equal Horgan's European record appearance tally (87 caps) when he runs out at Parc y Scarlets.
D'Arcy's inclusion sees Fergus McFadden switch to the right wing with Andrew Conway making way. Isa Nacewa and Ian Madigan complete the back-three, with Madigan continuing to deputise for the sidelined Rob Kearney in the number 15 jersey.
Out-half Jonathan Sexton, meanwhile, is just one point away from passing the 350-point mark in the Heineken Cup. He kicked three penalties in last Saturday's 9-6 win over Exeter Chiefs.
The other personnel change to the team that started against Exeter sees hooker Sean Cronin, a second half replacement last weekend, join fellow Ireland internationals Cian Healy and Mike Ross in the front row.
Leo Cullen leads the team and is named again alongside Galway man Damian Browne at second row, with Jamie Heaslip, Shane Jennings and Kevin McLaughlin again forming the back row unit.
Speaking ahead of the Pool 5 clash with the Welsh region, O'Driscoll said: "It wasn't my greatest game last week. What that does is drive you on to right the wrongs of disappointments - albeit we did win the game - and work on those things during the week and try and get them right on the Saturday.
"I've done that for years. Any time I've felt I've been a bit below par, I've tried to come out the following week and not force things.
"It's not about trying to work miracle plays, it's about doing simple things well and trying to be a cog in the wheel for a victory.
"We are working hard, of that there is no doubt. Guys are training hard, there are a lot of extras going on and sometimes it is just about taking your eye off the small things and taking things for granted a little bit.
"Last week's game allows you to focus a little bit and not take those things for granted."
The vastly-experienced centre added: "The Scarlets definitely have a talented back-line with some big ball carriers. They have a lot of guys who have played for Wales and have played well recently.
"It is not just a back-line thing. It is about pressure from the whole team when they have the ball and making sure we limit them when we can and play smart when we have the ball."
LEINSTER (v Scarlets): Ian Madigan; Fergus McFadden, Brian O'Driscoll, Gordon D'Arcy, Isa Nacewa; Jonathan Sexton, Eoin Reddan; Cian Healy, Sean Cronin, Mike Ross, Leo Cullen (capt), Damian Browne, Kevin McLaughlin, Shane Jennings, Jamie Heaslip.
Replacements: Richardt Strauss, Heinke van der Merwe, Jamie Hagan, Devin Toner, Jordi Murphy, Isaac Boss, Andrew Conway, Fionn Carr.