He was found guilty of participating in and funding terrorist acts and involvement in criminal conspiracy.
Malik told the court he gave up arms in the 1990s. He was convicted last week.
Tens of thousands of people have been killed in Muslim-majority Kashmir since an armed revolt against rule by India, which is mostly Hindu, erupted in 1989.
The court in the capital Delhi gave Malik, 56, two life sentences and five 10-year jail terms, all to be served concurrently, NDTV reported.
"Verdict in minutes by Indian kangaroo courts," Malik's wife Mushaal Hussein wrote on Twitter, saying he would never surrender.
Shops in some areas of Srinagar, the main city in Indian-administered Kashmir, were shut and police fired tear gas to disperse stone-throwing protesters outside Malik's residence. Mobile internet has been suspended in the region as a security precaution.
Prime Minister Shahbaz Sharif of Pakistan, which disputes India's claim to Kashmir, called it "a black day for Indian democracy".
"India can imprison Yasin Malik physically but it can never imprison [the] idea of freedom he symbolises," he tweeted.
India's National Investigating Agency (NIA), which deals with anti-terror crimes, had demanded the death penalty for Malik, the leader of the pro-independence Jammu and Kashmiri Liberation Front (JKLF). The defence had asked for life imprisonment.
Ahead of sentencing, he was escorted into the court surrounded by security forces.