Delhi Police set up 22,000 officers, concrete barriers and spike strips across the city after the CJP protest at Jantar Mantar.
The crackdown saw 250 trains cancelled, 45 metro stations shut, and internet suspended across the capital.
CJP leaders and hundreds of protesters were detained, including activist Abhijeet Dipke, who was held on a plane en route to Delhi.
Tharoor called the measures "regressive" and warned that turning the capital into a fortress would erode public trust.
He demanded the Delhi government lift checkpoints, restore internet and release detainees, and called for protection of women in the city.
A 23‑year‑old woman was reportedly held in a police cell for three hours after attempting to attend the protest, illustrating the crackdown's reach.