He revealed his decision in a long message posted on his Facebook page after a meeting to elect new executive members of the party's Krabi branch.
He said he had washed his hands of politics on Feb 5 - his 70th birthday - and was happy now to simply be a former MP.
Mr Pichet, a deputy finance minister in the Chuan Leekpai government between Nov 14, 1999 and Jan 6, 2001, said he personally loved and admired party leader Abhisit Vejjajiva and was willing to accept his general election boycott.
But he said he could not agree with Mr Abhisit's decision not to vote.
"No matter what the future of politics is, I would like to ask all party members not to obstruct an election, because we have never done this before," he wrote.
Mr Pichet also apologised for not persuading people from Krabi to join the protests in Bangkok, saying that he had wanted to prevent any loss of life.