<p>The methanogenic archaeon <i>Methanothermobacter marburgensis</i> offers a promising alternative to traditional bacterial systems for the sustainable production of proteinogenic amino acids (AAs), eliminating the need for sugar-based feedstock. In this study, we quantitatively examined AA excretion and consumption in fed-batch cultivation mode in bioreactors under varying ammonium (NH₄⁺) concentrations and gas compositions. <i>M. marburgensis</i> demonstrated excretion of a wide spectrum of AAs with distinct profiles shaped by nitrogen availability. While high NH₄⁺ concentrations suppressed total AA excretion, NH₄⁺ limited conditions triggered alanine accumulation followed by its re-assimilation, suggesting a regulatory mechanism linked to nitrogen stress. Moreover, carbon limitation and nitrogen excess resulted in the production of an AA pattern including asparagine. Despite lower overall productivity compared to engineered bacterial strains, <i>M. marburgensis</i> exhibited the unique ability to simultaneously excrete multiple AAs without requiring organic carbon input. These findings advance the feasibility of using methanogens for AA bioprocessing and the development of archaea as next-generation microbial cell factories.</p>