After marriage you will automatically obtain a new status, known as Domicile, and this overrides all visa requirements. Therefore no visa or permit will be required for you to enter, reside and work in Namibia.
However, as a legal process, it is recommended to apply for Certificate of Identity. This is a one page certificate issued by the Ministry of Home Affairs which serves as documentary confirmation of your domicile status. The reason for is this is that when you finally obtain Domicile status, there are no stamps in your passport and institutions such as banks will request for āsome form of document from Namibian governmentā, therefore the Certificate of Identity is used for that purpose. Further down the line, the certificate of identity will also serve for the purpose of applying for Permanent Residence and also Namibian citizenship.