The work was previously split between the Omnicom agency and WPP-owned rival Maxus.
In 2011, when SC Johnson consolidated its global media buying with Maxus, it allocated planning duties so that the two media shops worked with their sister creative agencies, Omnicom's BBDO and WPP's Ogilvy & Mather.
The two creative agencies remain in place and Maxus' hold on global media buying is unaffected.
An SC Johnson spokesman said: "In the course of renewing contracts with our advertising agencies, we have made a decision to have one global media planning agency, which will be PHD.
"We are currently working on a transition timeline. We anticipate completing the transition by spring."
PHD also runs Unilever’s global planning business, but this is from London, so SC Johnson’s choice of PHD to run its global planning from the US maintains the "Chinese walls" between clients.
According to Kantar, SC Johnson spent £150 million ($228 million) on media in the US alone in 2013.
In 2011 the UK account was worth £9 million.