In a statement today, he said he was forced to leave as a reconciliation was not possible.
He said the state DAP committee under Wong had initially wanted to sack him. He was then referred to the DAP national disciplinary committee which handed down a three-month suspension without calling him in to defend himself.
According to Bosi, the suspension period ends at the end of the month. His resignation, which was officially tendered on Aug 24, will take effect on Aug 31 tomorrow.
In April, Bosi threatened to run as an independent if he was dropped from his state seat in the 14th general election (GE14).
He said he had sought clarification from Wong over the matter, but that Wong could only tell him that he could not confirm if Bosi would be picked as a DAP candidate.
Bosi won the Kepayan seat in the 2013 general election with a 7,000-vote majority in a four-cornered contest.
Rumours had been circulating over his intention to quit the state chapter of DAP since August last year.
In his statement today, he said he would remain as an independent lawmaker for now until he decides on a local party that fights for the indigenous people and the people of Sabah.
He added that he bore no grudges against DAP or its leaders, and thanked them for the opportunity to run for the party.
Bosi is the third Sabah DAP leader to quit since the 2013 election.
Likas assemblyman Junz Wong, who was Sabah DAP secretary, resigned from the party on Oct 2 last year and joined Parti Warisan Sabah.
In 2013, Luyang assemblyman Hiew King Chiu left DAP to join MCA.