It follows shortly after the departure of the charity's assistant director of comms, who is returning to newspaper journalism.
Sharma (pictured) is currently head of strategic comms (international) in the Prime Minister's and Cabinet Office communications team.
Prior roles include head of comms for criminal justice system reform at the Ministry of Justice; head of policy and comms across South Asia for the Department for International Development; and strategic comms in southern Afghanistan with the Ministry of Defence, a role which he described in a 2006 piece in PRWeek.
He had worked for the Metropolitan Police and agency Weber Shandwick earlier in his career.
Sharma will report to Barnardo's strategy and performance director Adam Pemberton, who sits on its leadership team.
The comms chief role at the charity had previously been held on an interim basis by Nick Gammage since the departure of Gill Holmes to Chelsea and Westminster Hospital NHS Foundation Trust last year.
Sharma told PRWeek that priorities in the new role would include "using my experience of how comms can drive policy outcomes", supporting Barnardo's 10-year corporate plan initiated in 2015, and making sure that the charity's work "isn't compromised" by recent safeguarding scandals that have tainted the not-for-profit sector.