<p><i>Arthrospira platensis</i>, commonly known as spirulina, is a photosynthetically efficient cyanobacterium used for the production of nutritional supplements, biofuel, wastewater treatment, and CO₂ sequestration. These traits and uses make it a candidate for bioregenerative life support systems for space travel and future habitats. However, <i>A. platensis</i> lacks a robust cryopreservation method for long-term storage of viable cells, and genetic stocks are currently sub-cultured for maintenance. Here, we report an efficient cryopreservation method for the <i>A. platensis</i> strain NIES-39 and adapt this method for an upcoming spaceflight experiment. Seven cryoprotective agents were tested to preserve viable <i>A. platensis</i>. We found that a combination of dimethyl sulfoxide and trehalose additives to Zarrouk’s media protected trichome viability for extended storage periods at −80 °C. Throughout 1 year of frozen storage, we observed equivalent viability of cryopreserved cells in comparison to non-frozen cultures. Equivalent cryopreservation was demonstrated with multiple volumes of frozen culture, culture containers, and thawing methods to adapt the method for delivery and return of viable NIES-39 for the Space Algae-2 experiment on the International Space Station. The method requires minimal resources, employs simple freezing and thawing procedures, and could be implemented in commercial production to preserve genetic stocks.</p>