Lumengo was naturalized as a Swiss citizen in 1997 in Fribourg, and was elected to the Biel municipal council in 2004, and in 2006 to the cantonal council of Berne. In the 2007 federal election, he was elected to the Swiss National Council, as the country"s first national councillor of African origin (although there had been a councillor of mixed Swiss-African ancestry before: Tilo Frey, served 1971–1975), and the first former asylum seeker to be elected into the council. On 19 February 2010, Lumengo was investigated for voting irregularities.
While admitting to helping voters fill in their ballot papers in 2006, he rejected all accusations of trying to falsify the results.
Instead, he appealed the verdict and left the Social Democratic Party, announcing he would retain his seat in the National Council as an independent politician.