The deal was signed in December last year and had been awaiting regulatory approval.
Since then, Mukesh Ambani-controlled Reliance has been selling stakes in its digital unit to blue-chip companies, raising billions of dollars, to cut debt.
The finalisation of the deal also marks a foray into the fast-growing telecom market in India, which, in recent years, has been upended by the launch of Jio, Reliance's telecom arm, whose cut-price packages have turned it into the country's biggest telecom carrier by subscribers.
With the number of people using the internet in the world's second-most-populous country rising, the infrastructure that would widen its accessibility is a key building block.
"The portfolio offers resilient income and long-term value given India's attractive data demand growth outlook as 4G and smartphone penetration is still very low," said Ang Eng Seng, GIC's chief investment officer for infrastructure.
The investment by the group is for around 135,000 communication towers used by Reliance's telecoms venture Jio Infocomm, GIC said in a statement.
"While we remain cautious in this period of high uncertainty, we continue to seek good, long-term opportunities in India," Seng said.
(Reporting by Nikhil Kurian Nainan in Bengaluru; editing by Christian Schmollinger and Gerry Doyle)
