Muthalik was welcomed into the party fold in the presence of state party president Prahalad Joshi, former Chief Minister Jagadish Shettar and former Deputy Chief Minister K S Eshwarappa at a function here.
Muthalik later told reporters that he joined BJP with the objective of ensuring that Narendra Modi becomes the next Prime Minister.
Muthalik, who was arrest after the incident, had claimed that their actions were "aimed at protecting the women". The then Karnataka chief minister B S Yeddyurappa had said the Ram Sena had "nothing to do" with BJP or the Sangh parivar.
Muthalik has had a love-hate relation with BJP, which was evident when the saffron party had accused him of misusing Modi's name for raising funds. He joined RSS in 1975 and Shiv Sena in 2005, but left the latter in 2006.
More From This Section
BJP and Sangh Parivar leaders feel Muthalik's entry into the party can tilt the scales, especially in Belgaum, as people divided on the basis of mother tongues Kannada and Marathi, could come together under the Hindutva plank.
BJP leaders also feel his entry will benefit the party in other parts of the district and neighbouring districts.
The hardcore Hindutva leader is facing several cases, including one relating to promoting enmity between two communities.
Congress slammed BJP's move saying that its leaders, including Sushma Swaraj have been talking about women's empowerment but their party was now "glaringly opposing women's emancipation".
"You can see this is height of opportunism and I think that women across the country should take a very decisive call on this.