Blackie joined the WPP-owned Blue State Digital in 2011. The digital agency worked on Barack Obama’s first presidential campaign and counts the Labour Party among its clients.
He previously founded the digital team at the PR company Blue Rubicon.
Mahoney, who has been at LBi for three years, previously worked at OgilvyOne New York in 2005.
Both will report to Ann Higgins, the UK head of strategic services at OgilvyOne Worldwide.