Narayanaswamy, who recently joined Congress, defeated Karnataka Pradesh Congress Committee Secretary GC Chandrashekhar by 66 votes after garnering 180 votes, Congress leader M Ramachandrappa said.
Chandrashekhar was reportedly backed by KPCC President G Parameshwara.
IIM Professor and son of former Assembly Speaker, the late M Venkatappa, Rajiv Gowda, and former MLA NL Narendra Babu managed only 69 and 40.5 votes, respectively, with a total of 476 eligible voters having taken part in the process, he said.
Except for Narendra Babu, all candidates who contested the primary are from the Vokkaliga community, which has a good presence in the constituency.
Narayanaswamy, who is said to be backed by Chief Minister Siddaramaiah, has been contesting polls for more than the last 20 years, his only success being when he defeated former Railway Minister CK Jaffer Sharief.
The only other seat in Karnataka for which a primary was held by Congress is Dakshina Kannada, where former KPCC chief Janardhan Poojary emerged winner.