The rising status of English as a global language prompts a call for a paradigm shift in English language teaching in order to correspond to the new sociolinguistic landscape. However, studies related to English language assessment, which can catalyze the transformation especially in a test-oriented context like Thailand, remain limited. This mixed-methods study aimed to explore the perceptions and practices of 61 secondary school teachers regarding adopting Global Englishes (GE)-informed assessment by using a questionnaire, documentation, and semi-structured interviews. It was found that the participants expressed positive perceptions towards adopting GE principles when designing their classroom-based assessment, especially in the domains of speaking, listening, and the involvement of non-native English-speaking teachers in test design and development. However, little were GE principles reflected in their assessment practices. Themes, such as extensive use of standardized proficiency tests and native speakerism in test constructs, which are considered major challenges for successful implementation of GE, emerged. The findings contribute to a better understanding of the current status of GE-informed assessments in the context of Thailand and serve as a foundation for further developments in this field.