Chris Heaton-Harris said the inquiry would look at whether the attack, which saw 29 people killed and hundreds injured after the bomb exploded in the Tyrone town on August 15, 1998, could have been prevented.
Omagh Councillor Mr Donnelly said it marked another step in the long journey of the families of those killed.
“First and foremost, my thoughts are with the Omagh families. They suffered the greatest loss imaginable and yet have campaigned bravely every step of the way since, all to pursue truth and justice, concepts which should be a given to every victim in our society,” he said.
“Today’s announcement is another step towards that and another vindication for the campaigners. The Omagh bomb was the darkest day in the history of our town but the news of an independent statutory public inquiry being established brings a glimmer of hope the questions being asked since 1998 will finally be answered.
“Alliance is proud to stand alongside the families in calling for the dissident republican terrorists who carried out this atrocity to be brought to justice, and full openness and transparency given to the circumstances in which it took place.
“The sad fact is, the UK Government’s plans to introduce an amnesty would prevent other victims and their families from accessing the truth and justice they are entitled to. I would urge the Government to reflect on this fact and scrap its Legacy Bill.”