 Mbemba has been President of the Union for Progress (UP), a political party, since its founding in October 1990.He participated in the 1991 National Conference and headed the committee for the drafting of internal regulations at the National Conference.At the end of the National Conference, he was appointed as Minister of Justice and Administrative Reform in the transitional government of Prime Minister André Milongo, serving in that post from June 1991 to June 1992.