He added that the body would give Asean "more room for manoeuvre" when dealing with military-ruled Myanmar, whose human rights record has been widely criticised.
But he said the grouping would not impose sanctions or implement other punitive measures on states with a poor record on human rights.
Critics have said Asean's long-standing policy of non-interference in the internal affairs of its 10 members undermines any efforts to improve rights in the region.
Rafendi Djamin of the Asean Task Force on Human Rights, a grouping of non-governmental organizations from the region, called the new commission "toothless" and said nearly 300 civil society groups had urged Asean officials to address its shortcomings.
He said activists planned to discuss their concerns with Abhisit on Tuesday.
Myanmar has been Asean's so-called "problem child" since it was admitted to the bloc in 1997, with the group under pressure from the US and EU to take a tougher line on the country's military rulers.
Officials attending the summit admitted that Myanmar's human rights record was impeding Asean's progress and image.
"Without a resolution of the issue of Myanmar, Asean will continue to have a burden on its lap to explain to the world," Surin Pitsuwan, the Asean secretary-general told a news conference.
Among its 10 members, the bloc includes communist Vietnam and Laos, as well as Myanmar, which currently holds more than 2,000 political prisoners including opposition leader Aung San Suu Kyi.
She is currently on trial after allegedly violating the terms of her house arrest and faces up to five years in jail if convicted.
On Sunday, authorities in Myanmar detained dozens of opposition party members as they returned from ceremonies marking the death of General Aung San, Aung San Suu Kyi's father and the country's independence hero.
They were later released.
The launch of the human rights body comes as the US secretary of state is scheduled to arrive in Thailand on Tuesday, for security talks expected to focus on both Myanmar and regional concerns over North Korea's nuclear programme.
Hillary Clinton will attend the Asean Regional Forum, which follows the foreign ministers' meeting.
Clinton's attendance is being viewed as sign of renewed US priorities in the Asia-Pacific region under the Obama presidency.
A joint communiqué by Asean ministers on Monday expressed "grave concern'' over North Korea's nuclear programme following its recent tests of a nuclear device and several short-, medium- and long-range missiles.