"GMP certification means we've moved a long way down the path to being allowed to manufacture products," he said in a statement.
The next stage is to submit a new medicinal cannabis product application to the Medicinal Cannabis Agency.
Once that process is complete, Mitchell anticipates being able to supply product for the domestic market by early 2022.
Manufacturing will take place Rua's purpose-built facility in Gisborne and the compounded CBD oil will be available in New Zealand as a prescription-only medicine.
Rua's certification comes after a series of delays.
CBD oils are commonly prescribed in New Zealand for pain, epilepsy and anxiety.
Germany is the largest single market for pharmaceutical) grade cannabis globally.
Clinicians there can prescribe medicinal cannabis for a variety of conditions, many of which are covered by the statutory health insurers.
Shares in Rua Bioscience debuted on the NZX one year ago at 70c cents, a 20 cent, or 40 per cent premium to its 50 cent issue price.
The stock last traded at 41.5c, up 2.5c or 6.4 per cent.
Midwest Pharmaceutics NZ Limited, NZX-listed Cannasouth's wholly owned subsidiary, has GMP Certification for packing and wholesale supply of medicines.
Cannasouth said it is progressing with its GMP certification for own-manufactured cannabis-based products and would update the market with this timeline "in due course".
The company is also in the process of having three imported own-brand GMP medicinal cannabis products assessed by the Medicinal Cannabis Agency for distribution.
Unlisted medicinal cannabis company, Helius Therapeutics, was issued with the industry's first GMP certificate by MedSafe in July.