Born into a farmer family from north Gujarat, Karsanbhai finished his B.Sc. in Chemistry at age 21 and worked as a lab technician, first in the New Cotton Mills, Ahmedabad, of the Lalbhai group and then at the Geology and Mining Department of the state Government. In 1969, Karsanbhai started selling detergent powder, manufactured and packaged in his backyard. This was an after-office Business - the one-man company would bicycle through the neighbourhoods selling handmade detergent packets door to door. At a price of Rs. 3 per kg, (one third the price of leading detergents), it was an instant success. Karsanbhai branded his detergent soap, Nirma, after the name of his daughter. After three years, Karsanbhai felt confident enough to quit his job. Later he said, "The lack of any such precedent in my family made the venture fought with fear of failure. But farmers from North Gujarat are known for their spirit of enterprise." Karsanbhai set up shop at small workshop in an Ahmedabad suburb. The Nirma brand quickly established itself in Gujarat and Maharashtra.

In 1990, the Federation of Association of Small Scale Industries of India (FASII), New Delhi, awarded him the 'Udyog Ratna' award. The Gujarat Chamber of Commerce felicitated him as an 'Outstanding Industrialist of the Eighties'. He has served twice as Chairman of the Development Council for Oils, Soaps and Detergents.

In 1995, Karsanbhai started the Nirma Institute of Technology in Ahmedabad, which grew into a leading engineering college in Gujarat. An Institute of Management followed, with the entire structure being consolidated under the Nirma University of Science and Technology in 2003, overseen by the Nirma Education and Research Foundation. The Nirmalabs education project, aimed at training and incubating entrepreneurs, was launched in 2004.

In 2001, Karsanbhai was awarded an honorary doctorate by Florida Atlantic University, recognizing his exceptional entrepreneurial and philanthropic accomplishments.

The high quality and low price of the detergent made for great value. Fuelled by housewife-friendly advertisement jingles, Nirma revolutionized the detergent market, creating an entirely new segment in the economy for detergent powder. At the time, detergent and soap manufacture was dominated by multinational corporations with products like Surf by Hindustan Lever, priced around Rs. 13 per kg. Within a decade, Nirma was the largest selling detergent in India. Since production was labour-intensive, Nirma also became a leading employer (employing 14,000 people 2004). Made without some phosphates, Nirma was also somewhat more environment friendly.

In 2009, Karsanbhai was ranked #92 by Forbes magazine, for the list of India's richest persons.

Patel has been conferred with Padma Shri Award for the year 2010. The award was formally conferred by the President of India Mrs Pratibha Patil.

It was also announced on June 7, 2013 that he bought 40 crores six-seater chopper. After Adani Group chairman Gautam Adani and Zydus group promoter Pankaj Patel, Karshanbhai is the third Ahmadabad-based industrialist to buy a chopper.

In 2017, Karsanbhai was ranked #38 by Forbes magazine, for the list of India's richest persons ($ 640 million).