Vishwamitra Jayanti is observed in Bhadrapada Month. In 2020, Vishwamitra Rishi Jayanti date is August 23, Sunday.
Reportedly, Vishwamitra Rishi Jayanti falls on Bhadrapada Shukla Panchami (Rishi Panchami).
Brahmarshi Vishwamitra is one of the most famous rishis of ancient India. Vishwamitra is mentioned in various divine texts and Puranas. He has also authored some portions of the Rigveda. His birth name is Kaushika.
The story of Vishwamitra is found in the Valmiki Ramayana. Mahabharata also tells about the history of Vishwamitra.
Here is the birth story of Vishwamitra Maharshi (Vishwamitra Janma Vrittantha).