O'Neill, who started this month, has been tasked with helping to strengthen Edelman's brand strategy capabilities by creating work "grounded in insights and data".
That is according to Edelman general manager Ruth Warder, who said: "Michele is one of the industry's best thinkers. This hire is a further step in Edelman's journey, demonstrating our commitment to deliver audience-first work grounded in insights and data that drive business growth."
Reporting to Warder, O'Neill will sit within the agency's UK brand team, which includes more than 100 PR professionals, creatives, strategists and planners.
O'Neill said: "In a world where we now see behind the brand; trust, integrity and transparency are the attributes that matter. Edelman and its practitioners sit at the heart of where the real influence lies with brands, business and people; creating relevant conversations that are earned, not bought."
Prior to joining Edelman, O'Neill was director of strategy at VCCP in Sydney between 2014 and 2017. She was also chair of Australian industry body The Agency Circle.
O'Neill held the position of global strategy director at IPG agency Lowe and Partners between 2001 and 2011. She joined the agency having spent 10 years at Ogilvy & Mather, latterly as global planning director.
Edelman is the biggest agency in the UK, with revenues in excess of £60m last year, according to the 2017 PRWeek Top 150 UK.