The throng of protesters chanted “We don’t want military dictatorship. We want democracy,” in the main city, Yangon, as they rallied in more than a dozen different cities.
The demonstrations in Yangon on Sunday were the largest since the so-called Saffron Revolt of 2007 when thousands of monks in the country stood up against the military regime.
After a day-long blackout, internet access has now been restored.
The army held power after claiming, without evidence, declaring that the November election was fraudulent.
The rulers had proclaimed a state of emergency for a year and were hunkered down in the capital, Nay Pyi Daw.
Many leaders have been under house arrest from National League for Democracy Party (NLD) leaders such as Ms Suu Kyi other leaders, and President Win Myint.
People, in Yangon, donned red shirts, the colour of Ms Suu Kyi’s party, and held red balloons, while cars. The three-finger salute was flashed by many, a gesture of rebellion toward authoritarianism in the country.
The internet shutdown imposed by the military failed to curb the protesters. “Respect our vote,” read one banner, in reference to the NLD’s landslide win in November.
Throngs of people surged in the city centre towards the Sule Pagoda whereas police cars and policemen were deployed outside Yangon University in police uniforms.
However, there are no reports of violence.
“First, we don’t want to go back to military rule. We don’t want to live in fear. Secondly, we want Mother Su to be freed from being under detention unjustly,” a protester told the BBC. “And third, we want to root out the system where soldiers take civilian administrative positions.”
In Nay Pyi Daw and Mandalay, the country’s second-largest city, smaller protests were also held. There have been rumours of shots being fired in Mawlamine, but no-one was injured.