Grab operates ride-hailing services across 8 countries in Southeast Asia, matching drivers with passengers via a mobile app.
The firm also operates mobile platforms that offer payment solutions, food delivery and online shopping.
The Japanese financial services company first invested in Grab in 2016 and said that the renewed partnership will address the “increasingly demanding and diverse needs of the ride-hailing industry."
The firm said the investment will also enable Grab Rentals – the Grab unit that leases cars to private-hire drivers – the ability to "offer more flexible-term rentals and other new products.”
Grab is in the midst of its series H funding round, which is being led by Japanese car maker Toyota with a US$1bn investment.
The latest investment by Tokyo Century pushes the total sum raised in the round so far to above $3bn.
“Tokyo Century will leverage its financial expertise accumulated over many years in Japan through Grab’s platform to address increasingly demanding and diverse needs of the ride-hailing industry,” Tokyo Century said in a statement
“With the latest investment, Grab Rentals will further improve its driver-partners’ experience by expanding its product offerings including flexible-term rentals and an upcoming electric vehicle fleet.”