After 10 years in Yemen, but still a 20-something years old young man, he returned to India, armed with these insights and a vision for building a business empire. He started a company called "Majin" together with Champaklal Damani, his second cousin, who lived with him in Yemen: they initially focused on importing polyester and exporting spices. Due to fights and divergencies in business, a few years later, the two cousins ended their partnership and Ambani started his own business: he founded Reliance Commercial Corporation. By the 1970s, he had shifted his focus to textiles, from his previous experience, establishing the brand "Vimal", which became a household name in India. In 1977, while Hollywood released a sci-fi movie, called Star Wars, which would shape the world of cinema and popular culture forever, the 40-years-old Ambani Sr. launched the public offering of Reliance Industries: the listing of his company on the Stock Market, something more sci-fi than Star Wars at the time, was a game-changer, making it one of the first Indian companies to tap into the equity market, and Dhirubhai a beloved figure among investors. This IPO was a landmark event in Indian corporate history, setting the stage for the future expansion of Reliance.

The 1980s and 1990s were a period of rapid expansion for Reliance Industries: under Dhirubhai's leadership, the company diversified into petrochemicals, refining, and eventually oil and gas exploration, somehow going back to its origins. Reliance also found itself at the epicentre of a stock battle: ahead of a rights issue, the Bear Cartel, a group of stockbrokers from Calcutta, started to short sell the shares of Reliance. To counter this, others stockbrokers referred to as "Friends of Reliance" started to buy the short-sold shares of Reliance Industries on the Bombay Stock Exchange: it was such a financial earthquake the Stock Exchange was closed for three business days. He was then disclosed that Mr. Ambani lent shares, which would then be short-sold, to the same Cartel Group, his enemies. He made a lot of money in the speculation.

After the Stock Wars, many questions were raised in India about Ambani and his powerful empire. How a until-a-few-years earlier yarn trader was able to set-up such a complex scheme. The finance minister, Pranab Mukherjee informed the Indian Parliament that a foreign investor, in 1982-1983, had pumped 220 million Rupees in Reliance (some 20 million Pounds at the time). Curiously, those investments were routed via companies with strange names such as Crocodile, Lota and Fiasco, all of them registered in the Isle of Man, a notorious British tax haven. An investigation led by Bank of India never found any wrongdoing. Years later, the construction of the Patalganga plant marked Reliance's entry into the petrochemicals sector, while the Jamnagar refinery, opened in 1999, became one of the largest in the world, before Saudi Aramco came into the stage. Dhirubhai's vision extended beyond just business. He understood the importance of building a robust infrastructure and was instrumental in developing a comprehensive supply chain network that spanned the entire country. This network ensured the seamless flow of raw materials and finished goods, significantly boosting Reliance's efficiency and profitability: as of today, the conglomerate shows 120 Billion Dollars in revenues and some 10 Billion in net income.

In 1986, Ambani suffered a serious stroke which paralyzed one of his hands: following this near death experience, he decided to hand over the control of Reliance to his sons: Mukesh and Anil. The two brothers, as always happen between heirs, did not get along very well. Sixteen years later, on June 2002, Ambani was rushed to Breach Candy Hospital in Mumbai, after he had another stroke: he we was into a coma and died a week later. India mourned his most prominent industrialist. Two years later, Mukesh admitted having different views with his brother Anil over Reliance ownership: it was a polite way for hard issues.The group was split into Reliance Industries Limited, run by Mukesh, and Reliance Anil Dhirubhai Ambani Group, offered to Anil. Their father democratized the stock market by encouraging ordinary Indians to invest in Reliance. This created a massive base of loyal shareholders who were personally invested in the company’s success. By the time of his death, Dhirubhai had transformed Reliance into a conglomerate with interests in textiles, petrochemicals, and telecommunications.