The move, which UBM called a "significant step" in its ‘events first’ strategy, is set to see $371.2m (£245m) returned to shareholders through a special dividend on completion.
The agreement is subject to regulatory clearance in the US and requires approval from UBM shareholders. The deal is expected to complete in the first quarter of 2016.
Since last autumn, Cision has been on an acquisition spree, snapping up companies such as Viralheat, Visible Technologies and media intelligence and data insight specialist Gorkana Group.
Cision and Vocus officially combined under the former’s brand last October.
Peter Granat, CEO of Cision, said: "The addition of PR Newswire to Cision's growing portfolio represents a key milestone in our mission to create the most comprehensive platform for managing the communications life cycle effectively. PR Newswire's outstanding reputation and global reach add another valuable dimension to the quality suite of products our clients have come to expect from Cision."
UBM chief executive Tim Cobbold said: "Today's announcement represents a significant step in the execution of UBM's ‘events first’ strategy, the objective of which is to become the world's leading focused b2b events business. The board is confident that this transaction realises excellent value for our shareholders."
He said the disposal will mean more than 80 per cent of UBM’s revenues will be generated by events.
