Ten allegations had been made against the officer during his career before his encounter with Mr Tomlinson, who later died.
Metropolitan Police Deputy Assistant Commissioner Maxine de Brunner said: "Pc Harwood had previously served with the Metropolitan Police Service as well as Surrey Police. The details of his previous employment were examined at the inquest into Ian Tomlinson's death.
"It is clear that insufficient recording and checks meant that detailed information regarding the officer's misconduct history was not shared at key points. We got that wrong.
"Since then there have been huge changes to vetting processes. Now, all applicants, including officers applying to becoming police staff, as well those re-joining or transferring from other police services, are formally vetted and this involves a full misconduct intelligence check.