The weekly paper was previously published by family-run William Trimble Limited, which has now been sold to the Ulster News Group for an undisclosed sum.
The sale also includes monthly title the Lakeland Extra.
Joanna McVey, managing director of William Trimble, said: “This is a new and exciting chapter in the history of one of Ireland’s most respected weekly newspapers.
“The acquisition by Ulster News Group will bring many positive benefits to our long-established title and its sister, the Lakeland Extra.
“As we face the challenges of a rapidly changing media marketplace, this is an opportunity to take advantage of the extensive experience and expertise of a group which has a broad range of local newspaper interests in Ireland and Great Britain.
“We feel that this acquisition is ideal for the Impartial, whereby the newspaper will retain its independence but also profit from an attachment to a larger publishing group.”
She added: “At local level there will be little if no visible change. The Trimble family connection will not be lost as I will remain as chairman of William Trimble Ltd, whilst Denzil McDaniel, the newspaper’s managing editor, will continue to make a valuable contribution at Board level as a director of the company.”
Dunfermline Press Group’s titles include the Alloa & Hillfoots Advertiser, Dunfermline Press & West of Fife Advertiser and the Stirling News. Its sister company, Clyde & Forth Press, publishes the Greenock Telegraph and a host of weeklies which includes the Clydebank Post and Helensburgh Advertiser.
The stable also has close links with Celtic News Group, which publishes several titles in the Republic of Ireland including the Meath Chronicle in Navan.
The Impartial Reporter was founded by William Trimble in 1825.