This study explores Thai bilingual speakers’ code-switching in a formal work setting. Although code-switching may appear to be random, there is an underlying choice which speakers decide upon when switching between languages: Language proficiency, the initial speaker’s language choice, the setting, and role relationships all contribute to these choices. This study investigates the factors contributing to code-switch decisions by participants within their specific work environment. The main findings show that adopting one language over the other depends on two main factors: first, the initial sequence of the interaction; second, the role relationship that the participants wish to maintain. This study has drawn upon the conversational approach and Auer’s sequential analysis to collect and interpret data from ethno-graphic observations, questionnaires, and semi-structured interviews.