Premier Yingluck Shinawatra's Puea Thai party launched rallies in its northern strongholds and on the outskirts of Bangkok, where several thousand supporters gathered for meetings.
"The Pheu Thai Party now is in election mode," deputy spokesman Anusorn Iemsa-ard announced.
"I am confident that the campaign will go smoothly - we are not the ones triggering conflict," said party leader Jarupong Ruangsuwan, adding that the party's election slogan would urge people to vote to "preserve democracy".
The embattled premier, who came to power in 2011, called snap polls in a bid to end a festering political crisis after protesters escalated their anti-government campaign to remove the Shinawatra clan from power.
More From This Section
Protesters claim that the government is controlled by Yingluck's fugitive brother Thaksin Shinawatra, who is in self-exile to avoid a prison term for a corruption conviction.
They have demanded that Yingluck should hand over power to an unelected "People's Council" to carry out reforms before the polls.
In eight southern provinces, the stronghold of the opposition, no candidates are running.
About a dozen people have died and scores wounded since mid-October in clashes between police and protesters led by opposition leader Suthep Thaugsuban.
The ongoing turmoil is the worst since 2010 when thousands of pro-Thakisn "Red Shirt" protesters occupied key parts of Bangkok. More than 90 people, mostly civilian protesters, died over the course of the two-month sit-in.