The former Indian finance minister Arun Jaitley, was confirmed dead in a hospital in New Delhi on Saturday aged 66, the government said.
He served from 2014 until elections earlier this year, Jaitley oversaw the sudden withdrawal of vast amounts of cash from circulation in 2016.
Modi said the controversial policy, known as “demonetisation”, would bring the black economy out of the shadows but it caused huge disruption and eventually almost all notes were returned to the banking system.
A lawyer-turned-politician, Jaitley was also in office for the introduction of a new nationwide goods and services tax (GST), which was better received despite teething problems.
Jaitley underwent a kidney transplant last year and stepped down in May after being diagnosed with cancer.
Modi tweeted on Saturday that Jaitley was a “political giant, towering intellectual and legal luminary”.
“He was an articulate leader who made a lasting contribution to India. His passing away is very saddening.”