The meetings brought Rubio face-to-face with the leaders of two of India's largest business groups, which have significant investments in infrastructure, energy, technology and manufacturing.
Adani Group has interests spanning ports, airports, power, logistics and infrastructure. The conglomerate has also been expanding its renewable energy and manufacturing operations as India looks to strengthen domestic supply chains and attract international investment.
Chandrasekaran heads Tata Sons, the holding company of the Tata Group, whose businesses range from automobiles, steel and information technology to aviation and electronics.
The Tata Group has been investing in semiconductor manufacturing and battery technology, two sectors central to India's ambitions to become a global manufacturing and technology hub.
Rubio's engagements come as India and the US seek to expand cooperation in energy, manufacturing, technology and investment.
Rubio heads to Reliance's Jamnagar complex
After the Mumbai meetings, Rubio travelled to Jamnagar to visit Reliance Industries' refining complex, the Vantara wildlife conservation centre, and the company's upcoming green energy giga factories.
Reliance's Jamnagar facility is the world's largest single-site oil refining complex, with a combined processing capacity of approximately 1.4 million barrels of crude oil per day.
The Jamnagar visit also includes Vantara, the wildlife rescue, treatment, and rehabilitation initiative developed by Reliance Industries and Reliance Foundation under the leadership of Anant Ambani.
Spread across more than 3,500 acres, Vantara focuses on caring for rescued, injured and threatened animals, alongside wildlife conservation activities.
Reliance's green energy push in focus
Rubio is also scheduled to visit Reliance's Dhirubhai Ambani Green Energy Giga Complex, an industrial project being developed across more than 5,000 acres in Jamnagar.
The complex is designed to house manufacturing facilities for solar photovoltaic modules, battery energy storage systems, green hydrogen electrolysers, fuel cells and power electronics.
The investment is part of Reliance chairman Mukesh Ambani's strategy to build an integrated clean energy business alongside the company's established oil refining and petrochemicals operations.
The planned facilities are intended to strengthen India's domestic clean energy manufacturing capabilities and reduce reliance on imported equipment.
(With inputs from PTI)