'Waris de Punjab' chief Amritpal Singh currently lodged in Assam's Dibrugarh jail under the National Security Act has won Punjab's Khadoor Sahib Lok Sabha seat defeating Congress's Kulbir Singh Zira by a margin of more than 1.5 lakh votes.
Amritpal Singh had fought the election as an independent candidate after he was arrested following the demand for a separate state for Sikhs.
A jailed Sikh separatist leader who stood in India's election won a seat in parliament on Tuesday with over 400,000 votes in what aides and relatives said was a sign of public anger over the "injustice" of his incarceration.
Amritpal Singh, 31, is in a high-security prison in the eastern state of Assam, nearly 3,000 km (1,900 miles) away from his constituency of Khadoor Sahib in the northwestern state of Punjab, where he ran as an independent.
Last year, Singh said he backed the creation of an independent homeland for his people in Punjab, decades after a Sikh insurgency killed tens of thousands in the 1970s and 1980s before it was stamped out.
Sikh separatism has made global headlines in the last year as Canada and the United States have accused India of being involved in assassination plots against Sikh separatists in those countries, charges New Delhi has denied.
"People have given such a huge victory in his favour to tackle the injustice he faces," Singh's lawyer Imaan Singh Khara said.
"He's got all the blessings. We will try to meet him in prison in the coming days and wish that he is also freed soon," Singh's father Tarsem, 61, said.
Sikh separatists have previously stood in Indian elections and won.
Singh was detained under a tough security law last year after he and hundreds of supporters stormed a police station with swords and firearms, demanding the release of one of his aides.
His supporters say Singh's movement only calls for adherence to religious teachings and tackling drug use among Punjabi youth. Sikhs comprise the majority community in Punjab but constitute just 2% of majority-Hindu India's 1.4 billion people.
"People who take up arms also know how to hold discussions and participate in democracy," said Karamjit Singh Sunam, a Singh campaign worker.
In 1984, Indian Prime Minister Indira Gandhi was shot dead by her two Sikh bodyguards over her decision to send the army into Sikhism's holiest shrine - the Golden Temple - to root out Sikh militants sheltering there.
