However, Mr. Donaldson cautioned the victorious UUP against seeing the result as indication of a revival in their electoral fortune.
He said, "Whilst we had an excellent local candidate in Paul Stewart, who successfully topped the poll, the loss of a significant portion of our vote to the TUV cannot be ignored."
Mr. Donaldson commended Mr. Stewart as a young man with a bright future in local politics who ran an excellent campaign and did well in his first electoral contest.
"As well as topping the poll," he said, "the DUP remains the largest Party in the Dromore area. I want to thank everyone who voted for Paul Stewart and the DUP in this election.
"However, the fact that over 700 traditional DUP supporters chose this time to switch their vote to the TUV reflects a concern in a significant section of the Unionist community that cannot be ignored. My sense is that many of these voters still support devolution in principle but they are clearly concerned by some of the imagery that has emerged from Stormont.
"They chose this by-election to make a protest with their vote and the message they are sending to the Party will not be ignored."
As MP, Mr. Donaldson gave a commitment to the people he represented that their concerns would be taken on board and acted upon.
"I want to restore the confidence of those who voted in protest for the TUV," he said, "as I believe that we cannot afford a further splintering of the Unionist vote.
"If this result were to be replicated across Northern Ireland then Sinn Fein would emerge as the largest Party and Martin McGuinness would become the First Minister of Northern Ireland.
"Therefore, splits of this nature are not in the best long-term interests of Unionism; the DUP must try harder to reunite Unionism."
Mr. Donaldson congratulated the UUP's Carol Black on her win but insisted her "narrow" victory, "totally reliant on transfers from across the political spectrum" amounted to yet another decline in their share of the vote.
"They may boast about their victory," he said, "but the UUP would be foolish to regard this result as marking the start of a revival in their electoral fortune.
"The further reduction in their share of the first-preference vote reveals an ongoing slide in their support base in an area like Dromore where they were once the dominant force just a few short years ago.
"The UUP failed to win back any of the ground they lost previously despite the difficulties for the DUP with their vote being split by the TUV on this occasion.
"The DUP will learn from this election and will heed the messages that are coming from the local community. We will continue to work in the local Council and in the Assembly in the best interests of everyone."