Her win could have a major impact on the working life of staff struggling to combine child care and career.
Governors at Langtree primary, in north Devon, struck a deal with Mrs Marshall,44, after she threatened to fight for pound;100,000 compensation.
She will work part-time after half-term but the arrangement will be re-considered in the summer.
Ian Poole, National Association f Head Teachers solicitor, said goverrnors, Devon council and Mrs Marshall would work to ensure that the arrangements were "to the benefit of the school, the children and parents".
A tribunal last summer found governors and Devon education authority guilty of sexual discrimination in denying her a job share. But the case dragged on after the council called for a time limit on the arrangement.
Governors had opposed the job share because the 80-pupil school was struggling, and they wanted "clear leadership by a single postholder".