Far-right Indian protesters angry at the launch of former Pakistani Foreign Minister Khurshid Mahmud Kasuri's book in Mumbai doused the event organizer with black ink on October 12.
Sudheendra Kulkarni said he was assaulted outside his home by a group of activists from the Hindu nationalist Shiv Sena party.
Kulkarni condemned the incident as an "assault on democracy" as he addressed the media in Mumbai, his face and hair covered in ink.
Shiv Sena's spokesman described the incident as a "nonviolent protest." The party has said it will not allow anyone from Pakistan to hold a public event in India.
The book was launched as planned amid heavy security.
India and Pakistan have been archrivals since gaining independence from Britain in 1947 and have fought three wars.
There are growing concerns over freedom of speech in India after the execution-style killing in August of M.M. Kalburgi, a leading secular scholar who had angered hard-line Hindu groups.
India's Culture Minister Mahesh Sharma criticized the latest attack, saying protests should be "within the democratic framework of our constitution."