The existing studies on e-government outsourcing pay attention to the factors that influence the service satisfaction of software service providers, and there is currently little research on how software service providers develop during different phases involved, which plays an important role in the e-government outsourcing projects. We apply the literature on business ecosystem and resource orchestration which may be crucial to the development of a software service provider to analyze a typical software service provider in the field of electronic tax outsourcing. In doing so, a process model of how a service provider makes resource orchestration as environments change and develops its focal capabilities is inductively derived that sheds light on the process from a niche player to be a keystone in three distinct phases. The process model reveals that the role of the software service provider within its ecosystem is evolutionary in nature. With above findings, this study provides practitioners a comprehensive and empirically supported framework and shows a successful process model of how to be a keystone within the e-government ecosystem.