This paper reports on a narrative inquiry of a Hong Kong female undergraduate student's second language (L2) learning experiences in an English-medium university in Hong Kong, with a focus on her participation in classroom oral activities and identity negotiation. Using ideas from situated learning theory and Norton's (2000) notions of identity and investment, the paper analyzes how the student negotiated her classroom participation and identities over the course of her studies in the university. Findings suggest that the student's classroom participation in the English-medium university appeared to be a complex and dynamic process which involved ongoing negotiations of identities, competence and membership in the classroom in response to the challenges she faced. It was found that the student's participation and identity (re)construction in the classroom were mediated by the contextual complexities in specific classroom communities and were contingent upon the agentive choices made by the student in investing in different classroom activities. Findings also indicate that the student's participation evolved over time alongside a changing sense of competence and showed signs of gradual yet non-linear progression from peripheral to full participation in the classroom. [Copyright of Applied Linguistics Review is the property of Walter de Gruyter GmbH]