Fanning impressed in the pre-season matches against Harlequins and Saracens and is brought in as cover in the back-line.
Conneely has a proven track record for Connacht at Under-18 and Under-20 level and the 20-year-old back rower has been rewarded for a good pre-season with inclusion in the senior squad.
Former Queensland Reds number 8 Ezra Taylor has been ruled out of the game after suffering a knock to his knee during his competitive debut against the Dragons.
"You have to expect a backlash and with our record over their they will probably be expecting to claim five points, conversely we are looking to improve our away form.
"We have set ourselves a good target for this week, that's the challenge and we're looking forward to it."
CONNACHT Squad (v Scarlets) - Backs (12): Cillian Willis, Frank Murphy, Miah Nikora, Ian Keatley, Fionn Carr, Keith Matthews, Niva Ta'auso, Tiernan O'Halloran, Aidan Wynne, Troy Nathan, Gavin Duffy, Darragh Fanning.
Forwards (13): Ronan Loughney, Brett Wilkinson, Sean Cronin, Adrian Flavin, Rob Sweeney, Jamie Hagan, Dave Nolan, Michael Swift, Bernie Upton, Michael McCarthy, Ray Ofisa, Mike McComish, Shane Conneely.