This paper reports on the development of complexity and accuracy in English as a Second Language (ESL) academic writing. Although research into complexity and accuracy development in second language (L2) writing has been well established, few studies have assumed the multidimensionality of these two constructs (Norris & Ortega, 2009) or endeavoured to make long-term observations on the course of their development (Vyatkina, 2012). Given that recent research in the field of Second Language Acquisition has moved towards a more holistic perspective on language learning and development (Larsen-Freeman, 2011, 2012), there is a need to consider the potential dynamics of the longitudinal development of these constructs in L2 writing. This study addresses this issue by exploring the dynamic unfolding of complexity and accuracy development in the academic writing of an advanced L2 learner during her postgraduate study in Australia. The results suggested that both complexity and accuracy displayed the characteristics of a dynamic system and their development was highly variable, non-linear, and idiosyncratic. Their interaction, too, was dynamic and changed over time. The findings in this study confirm and substantiate the Dynamic Systems Theory (DST) proposition of L2 developmental dynamics, including the development of L2 academic writing.