White is to become chairman of retailer The John Lewis Partnership.
She joined Ofcom in March 2015 from HM Treasury where she was Second Permanent Secretary.
Lord Burns, Ofcom chairman, said: “Sharon has been an outstanding Chief Executive for Ofcom and will be missed by the whole organisation.
“Under Sharon’s leadership, Ofcom has helped to deliver ultrafast broadband, widespread 4G mobile and now 5G, and became the first independent regulator of the BBC.”
“She leaves Ofcom as a regulator with a relentless focus on the consumer interest; making sure people and businesses can get the best out of their communications services.”
Sharon White said: “It’s been a huge privilege to lead Ofcom at a time when reliable, affordable communications have become essential. I will leave behind an organisation that is dedicated in its mission to make communications work for everyone.”
The Ofcom Board will now begin the process to appoint a successor.