Check out this webpage: http://www.doctrine.org/history/HPv2b14.htm#2-14-19-15
This is a history written in the late 19th century that describes the Servetus issue in great detail in chapters 19-22. It would probably be best to read some of the chapters preceding those to get an idea of what Calvin's Geneva was like. It is shown that Calvin's influence was very much on the wane during the time of the Servetus episode. In fact, Calvin was on the verge of being kicked out of the city. Calvin let the council know that Servetus had entered the city, in accordance with Genevan law. He wrote up the articles against Servetus. After that, Calvin had very little involvement.
"Therefore, without consulting Calvin, without even thinking of him, and viewing the question as a social rather than a theological one, and dealing with it as sedition rather than heresy...the magistrates of Geneva closed their Diet of the 26th of October with a decree condemning Servetus to death."