The CIPR would not reveal whether the decision for Farrington to leave lies with the body or with Farrington himself.
The CIPR is now conducting a series of strategic reviews and will confirm its plans for the management of the Institute shortly.
Farrington said: ‘I have been privileged to lead the Institute during a period in which it was recognised as the professional body for the PR industry in the UK. I am grateful to the hard-working staff, officers and members who have supported me as we worked to make the CIPR the voice of the profession.
‘I hope the CIPR will continue to go from strength to strength.’
Farrington was due to return to work in January after a six-month absence due to illness.
Last week, PRWeek revealed that the CIPR planned to make new appointments to its senior team. The news came after it was revealed in November that the CIPR made a loss of £700,000 last year.
CIPR president Jay O'Connor paid tribute to Farrington’s work at the CIPR: ‘During his tenure as director general, Colin has increased the membership, steered the Institute to Chartered Status, boosted our professional development activities and built up the CIPR brand in the UK and abroad.’