Besides being a famous physicist, he's also a great novelist.
Literal
Famous-[attributive-な] physicist be-[on-top-of-上に], he [topic-は] great-[attributive-な] novelist [also-でも] be.
~上に ('in addition to, on top of') is a formal connector adding a second attribute to the subject. Attaches to the attributive form of an adjective or noun+である. 小説家でも (noun + でも) marks 'also a novelist,' reinforcing the 'in addition to' framing. Formal essayistic register.