Parker will be replaced by Nik Antona, who will take on the leadership of the organisation following its members' weekend, AGM and conference to be held in Dundee in April.
Antona takes over from Parker, who is stepping down after 12 months in the role and after nine years as a member of CAMRA's national executive.
Parker was elected by her colleagues at the national executive meeting on 1 December 2017, taking over from Colin Valentine who had been in the role for eight years and a CAMRA member for more than 30 years.
She had been an active member of the organisation for 18 years prior to being elected chair and was previously national vice-chairman.
New chair Antona said: "I'm delighted and honoured by the confidence my national executive colleagues have shown in me by electing me to take over as chairman in April.
"Jackie has been a strong leader for the organisation and I am keen to carry on where she will leave off – making sure CAMRA is effective in its national campaigns, especially in seeing much-needed reform of the pubs code, calling for a review of business rates on pubs and campaigning to get a reduction in beer tax on pints served in pubs."
Parker outlined how long she had been involved with the organisation and how handing the mantle over was the right thing to do.
She added: "It is with great sadness that I choose to step down as chairman of the campaign. It's the right time, however, as I come to the end of my third term as a national executive member.
"I've spent nine years as a national executive member and served as regional director for three years prior to that.
"It's healthy for an organisation to refresh its leadership regularly and now is the time to step aside and give someone else the opportunity to lead the campaign."