This systematic review of quantitative research on Autistic identity identifies key factors associated with the development of a positive Autistic identity and its relationship with mental health and wellbeing. A total of 20 studies met the inclusion criteria, with 3,617 studies screened. Results indicate that receiving external autism acceptance and support is associated with a more positive Autistic identity. Individual factors were largely nonsignificant or inconclusive, highlighting the need for broad support that meets the needs of a range of Autistic people. Positive Autistic identity was associated with improved mental health and wellbeing. Peer support and self-directed support resources may be valuable mechanisms for supporting Autistic people to cultivate a positive Autistic identity. Future research should evaluate the long-term impacts of such support on identity development. Autistic identity is conceptualized as encompassing both personal and social aspects. Personal identity refers to how individuals define themselves and how this influences life choices, while social identity relates to belonging to a group and the sense of community. Identity development is a lifelong process, with adolescence and early adulthood being particularly relevant. Receiving an autism diagnosis can have a significant impact on one's sense of self, with varying reactions depending on the timing and context of the diagnosis. Factors such as external acceptance and support, self-esteem, and camouflaging/masking behaviors were significantly associated with Autistic identity. Higher levels of external acceptance and support were linked to stronger Autistic identity and greater perceived benefits of autism. Self-esteem was also significantly associated with Autistic identity, with higher self-esteem linked to greater pride in being Autistic and more positive perceptions of autism. The association between Autistic identity and mental health and wellbeing was significant, with positive Autistic identity linked to improved mental health and wellbeing. Anxiety, depression, and psychological distress were also associated with Autistic identity, with higher levels of internalized stigma and dissatisfaction with being Autistic linked to poorer mental health outcomes. The review highlights the importance of environmental factors, such as external support and acceptance, in shaping Autistic identity. Peer support and community involvement were found to be beneficial for Autistic people in developing a positive identity. Future research should focus on evaluating the long-term impacts of such support on identity development and exploring the role of intersectionality in shaping Autistic identity. Overall, the findings suggest that broad, inclusive support that addresses the diverse needs of Autistic people is essential for promoting positive identity development and mental health.This systematic review of quantitative research on Autistic identity identifies key factors associated with the development of a positive Autistic identity and its relationship with mental health and wellbeing. A total of 20 studies met the inclusion criteria, with 3,617 studies screened. Results indicate that receiving external autism acceptance and support is associated with a more positive Autistic identity. Individual factors were largely nonsignificant or inconclusive, highlighting the need for broad support that meets the needs of a range of Autistic people. Positive Autistic identity was associated with improved mental health and wellbeing. Peer support and self-directed support resources may be valuable mechanisms for supporting Autistic people to cultivate a positive Autistic identity. Future research should evaluate the long-term impacts of such support on identity development. Autistic identity is conceptualized as encompassing both personal and social aspects. Personal identity refers to how individuals define themselves and how this influences life choices, while social identity relates to belonging to a group and the sense of community. Identity development is a lifelong process, with adolescence and early adulthood being particularly relevant. Receiving an autism diagnosis can have a significant impact on one's sense of self, with varying reactions depending on the timing and context of the diagnosis. Factors such as external acceptance and support, self-esteem, and camouflaging/masking behaviors were significantly associated with Autistic identity. Higher levels of external acceptance and support were linked to stronger Autistic identity and greater perceived benefits of autism. Self-esteem was also significantly associated with Autistic identity, with higher self-esteem linked to greater pride in being Autistic and more positive perceptions of autism. The association between Autistic identity and mental health and wellbeing was significant, with positive Autistic identity linked to improved mental health and wellbeing. Anxiety, depression, and psychological distress were also associated with Autistic identity, with higher levels of internalized stigma and dissatisfaction with being Autistic linked to poorer mental health outcomes. The review highlights the importance of environmental factors, such as external support and acceptance, in shaping Autistic identity. Peer support and community involvement were found to be beneficial for Autistic people in developing a positive identity. Future research should focus on evaluating the long-term impacts of such support on identity development and exploring the role of intersectionality in shaping Autistic identity. Overall, the findings suggest that broad, inclusive support that addresses the diverse needs of Autistic people is essential for promoting positive identity development and mental health.