Male fertility is dependent on spermatogonial stem cells (SSCs) that self-renew and produce differentiating germ cells. Growth factors produced within the testis are essential for SSC maintenance but intrinsic factors dictating SSC response to these stimuli poorly characterised. Here we studied the role of GILZ, a TSC22D family protein and spermatogenesis regulator, in spermatogonial function and signalling. While broadly expressed in the germline, GILZ was prominent in undifferentiated spermatogonia and Gilz deletion in adults resulted in exhaustion of the GFRα1+ SSC-containing population and germline degeneration. GILZ loss was associated with mTORC1 activation, suggesting enhanced growth factor signalling. Expression of deubiquitinase USP9X, an mTORC1 modulator required for spermatogenesis, was disrupted in Gilz mutants. Treatment with an mTOR inhibitor rescued GFRα1+ spermatogonial failure, indicating that GILZ-dependent mTORC1 inhibition is critical for SSC maintenance. Analysis of cultured undifferentiated spermatogonia lacking GILZ confirmed aberrant activation of ERK MAPK upstream mTORC1 plus USP9X downregulation and interaction of GILZ with TSC22D proteins. Our data indicate an essential role for GILZ-TSC22D complexes in ensuring appropriate response of undifferentiated spermatogonia to growth factors via distinct inputs to mTORC1.