This study posits that, in the absence of extensive mandatory regulation and auditing, differences in internal and external corporate governance (CG) mechanisms will explain variations in choices concerning corporate sustainability reporting and the interrelated and underlying corporate sustainability performance (CSP). Specifically, we explore whether board monitoring effectiveness as a major internal CG mechanism and stakeholder engagement as a key external CG mechanism are positively associated with sustainability reporting quality (SRQ), compliance with generally accepted sustainability reporting standards (SRC) and guidelines, and CSP for a sample of Dutch firms that have voluntarily disclosed sustainability reports during the years 2012-2016. In addition to these direct effects, we also investigate the potential indirect effects of the CG mechanisms on SRQ and SRC via CSP and distinguish between nonlagged and lag effects. Using structural equation modeling, our results show that, in the short term, monitoring effectiveness positively affects SRQ and SRC. Stakeholder engagement positively affects SRQ and SRC in the short term and is positively related to SRQ via CSP in the longer term, indicating that active stakeholders, over time, may drive companies toward more sustainable business conduct. Finally, the findings that CSP is positively related to SRQ but negatively related to SRC provide further support for signaling and legitimacy theory, respectively. Companies with superior CSP disclose high-quality information on CSP to signal the firm's superior sustainability performance, whereas poor performing companies legitimize their inferior CSP by complying with more reporting standards, rather than by directly improving their underlying CSP.