Separately another red-shirt, Surachai Damwattananusorn, has been arrested on charges of insulting the monarchy.
The government has meanwhile extended implementation of the Internal Security Act for another month.
It is trying to contain continuing protests by both the red-shirts and the nationalist "yellow-shirt" protesters.
The decision to release all seven red-shirt leaders and a protest guard was a surprise. At most, two leaders were expected to be freed.
But the court ruled that unspecified new evidence made their temporary release possible - on condition that they did not incite or instigate any violence or disorder.
Among them are some famous names from last year's Bangkok protests - Natthawut Saikua, Dr Weng Tojirakarn and Kokaew Pikulthong.
These men dominated the stage as many thousands of red-shirted people camped out in the centre of Bangkok for two months.
After the army moved in for a second time last May, a total of 91 people had died and several hundred had been arrested.Electioneering
Scores of protesters remain behind bars, though the leadership is now free.
Analysts say this is probably an attempt at reconciliation by the government. It has said it wants to call elections before June.
But political turmoil here is not over. Another red-shirt leader has already said the protest actions would continue.
Conflict with Cambodia over a disputed border in the north is seen as another part of the complex electioneering now in full spate.
A more nationalist anti-government movement known as the yellow-shirts remain encamped near parliament and had been pressing for firm action against Cambodia.
It seems the government is trying to appease both their sentiments and those of the red-shirts, as a series of anniversaries of last year's protests approaches.
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