Ms Adam has been a Mid-Formartine councillor since 2017.
She said: “Representing the area has been an absolute honour and a privilege. My constituents have been fantastic, and I have endeavoured to help and support everyone in the ward to the very best of my abilities.
"I would also like to pay tribute to the ward community groups as well as council staff who have all contributed to my ability to support my constituents in Mid-Formartine, and not least through the difficult times we have endured.
“After a month of careful consideration, I have come to the conclusion that my focus should be entirely on my role as the MSP for Banffshire & Buchan Coast and I feel that the people living in Mid-Formartine deserve a full time representative as their councillor.
“Some politicians are able to successfully carry out both roles as a councillor and MSP.
"However, I have been very open about my commitments as a parent and carer.
"As always, individual circumstances play a part in any decision such as this.
“Whoever the people of Mid-Formartine choose to elect, I wish them the very best in representing the people in the ward to the best of their ability.”
Councillor Gwyneth Petrie, Leader of the SNP Group in Aberdeenshire, paid tribute to Ms Adam for her work as a councillor.
She added: “The group was delighted to see Karen elected as an MSP, and we very much look forward to seeing her progress in that role.
“We are, of course, disappointed to see Karen leave the group – she has been an integral and valued member, and will be a huge miss. We do, however, recognise that this is the best decision for Karen, and her personal circumstances. We wish her all the best for the future, and look forward to continuing to work with her, albeit in a different way.”
Ms Adam retained the Banffshire & Buchan Coast constituency for the SNP in last month’s election with a majority of 772 votes over Conservative Mark Findlater.
A by-election will be held to elect a new councillor for the Mid-Formartine ward.