Shailesh Kumar was born on 25 December 1963, Bariarpur, Munger district, Bihar. His father, Late Suresh Kumar Singh was also Member of Legislative Assembly from Jamalpur constituency(Bharatiya Jana Sangh Party) for two terms in 1975 and 1977. Kumar completed his Primary education in Philip High School Bariarpur. He graduated from Sahibganj College Jharkhand and pursued his post graduation (Master of Art) from R.D.&D.J. College, Munger in 1984.^[3][4]

After completing his degree he became History Lecturer in Asarganj College from 1989 to 1993. He started involving in social activities from 1985. He worked in many NGOs. He was also member of Red Cross society which is a voluntary humanitarian organization to protect human life and health based in India. He married Nootan Sinha on 2 July 1993. She is from Madhusudanpur, Muzaffarpur District. They have a son and 2 daughters.

In 1995, He joined Samta party under the leadership of George Fernandes and Nitish Kumar. He Contested election but lost from few margin. In 2000 he again Contested election from Independent party and came second position. Under the leadership of Nitish kumar when Janta Dal United party came to power in 2005, he was elected as Member of Assembly from Jamalpur Constituency. In 2010 again he won election from the same constituency. In 2015, he became the Minister of Rural Work Department till date.