The protesters are building barricades and occupying key road junctions.
The government has deployed 18,000 security personnel to maintain order.
The protesters, who began their campaign in November, want to replace the government of Prime Minister Yingluck Shinawatra with an unelected "People's Council".
They say Ms Yingluck is a proxy for her brother, former Prime Minister Thaksin Shinawatra, who was ousted by the military in 2006 and is currently in self-imposed exile.
Protesters allege populist policies from Thaksin-allied parties have created a flawed democracy.
Thaksin-allied parties draw considerable support from rural voters and have won the last four elections. The main opposition party is now boycotting the 2 February polls.
At least eight people have been killed since the protests began late last year. On Saturday, at least seven people were injured when unknown gunmen opened fire on demonstrators at the main rally site in Bangkok.
On Sunday night, an unidentified gunman attacked demonstrators at a protest site, shooting at least one man, officials said.
Police said a gunman also fired shots at the opposition party headquarters in a separate incident, although no casualties were reported.
'No win-win'
Huge crowds are expected to turn out for the demonstration on Monday. Protesters say they intend to achieve what they are calling a shutdown of the capital.
Seven major intersections have been blocked by the anti-government protest movement, which has erected stages and piles of sandbags across the roads, the BBC's Jonathan Head in Bangkok reports.
The government says it wants life to continue as normal through the shutdown and has ordered extra trains to run on the mass transit system and provided thousands of additional parking places outside the city centre, our correspondent adds.
Protesters also plan to surround key ministries and cut off their power supply in a bid to prevent them from functioning.
About 150 schools have been told to close.
The protesters say they will remain in place for several days - but say they will not target public transport or the airports, which were closed for several days by anti-Thaksin protesters in 2008.
At a rally on Sunday, protest leader Suthep Thaugsuban was defiant.
"I want to announce on this important night that the masses will not accept any proposals or negotiations," he told supporters, as quoted by the Associated Press news agency.
"In this fight, defeat is defeat and victory is victory. There is no tie. There's no win-win. There's only win on one side."
The government says it is deploying 8,000 soldiers and 10,000 police to keep order.
The military - which has carried out several coups in the past - has refused to rule out another one. Some fear an escalation of violence could lead to a military intervention.
The government has so far worked to avoid confrontation with the protesters.
Ms Yingluck had "ordered all police and military personnel to exercise utmost restraint and not to use all kinds of weapons in handling the protesters", the deputy prime minister said.
The political unrest is the worst to hit Thailand since the protests of 2010, which were against a government led by the current opposition party and left more than 90 people dead.
BBC
