The big second row arrived to Galway last Wednesday and was keen to get involved in training the very next day.
"Craig is keen and he's available. He was not supposed to start until next week, but pretty much the first day he came down he was ready to go," said Pat Lam ahead of the Newcastle game.
"I think it's a case of him letting the boys see he is keen to be here, which is great - to see the leader he is and the type of person he is."
Clarke's former Waikato team-mate Nathan White returns to the fray this weekend after siting out the 31-7 loss to London Wasps due to a small injury.
The province's forwards have been given another boost with the timely return of Connacht's record caps holder Michael Swift. The 35-year-old lock was declared fit to play in training early this week.
Returning out-half Dan Parks is joined in the backs by last weekend's lone try scorer, Eoin Griffin.
CONNACHT Squad (v Newcastle Falcons) - Backs (11): Tiernan O'Halloran, Shane Layden, Fionn Carr, Matt Healy, Brian Murphy, Eoin Griffin, Conor Finn, Dan Parks, Miah Nikora, Kieran Marmion, Frank Murphy.
Forwards (15): Sean Henry, Jason Harris-Wright, Rodney Ah You, Brett Wilkinson, Ronan Loughney, Nathan White, Craig Clarke, Michael Kearney, Michael Swift, Andrew Browne, John Muldoon, Willie Faloon, Jake Heenan, Eoin McKeon, George Naoupu.