Purpose Currently, online chat is in common use in e-commerce. By adding social interaction to the online context, companies hope to increase customers’ purchasing intentions. However, previous studies have not investigated how social presence is embedded in online business-to-business (B2B) chat conversations between buyers and sellers. Moreover, the functions of online chat in B2B sales have not been investigated. Design/methodology/approach The data was collected at a case company over the course of four years, from which the authors analyzed 157 online chat conversations between buyers (n = 157) and sellers (n = 9) with a theory-driven thematic analysis. In addition, data from the company’s customer relationship management system was collected to specify buyer types. Findings The results reveal that social presence was embedded in online B2B chat via buyers’ interactive, affective and relationship maintenance responses. Social presence differed depending on the type of buyer, with only existing customers having relationship maintenance responses. E-commerce B2B chat functions can be described as multiple and changing depending on the buyer–seller relationship stage. Research limitations/implications Having data only from one case company limits the results to one type of industry. Practical implications The results can be used in sales training and when developing online chat services. Originality/value Results bring scientific utility to B2B sales and marketing research, as the authors build a bridge between social presence, the existing theoretical model on B2B buyer–seller relationship development and online chat as a communication medium. Other researchers may use this understanding when exploring B2B buyer–seller interaction in different digitalized communication media.