Kalonji served as a delegate for the Katanga Cartel (an alliance between FEDEKA, BALUBAKAT, and ATCAR) at the Belgo-Congolese Round Table Conference in early 1960. Afterwards he ran the Cartel's office in Belgium for several months and attended the Economic Round Table Conference as an observer. In May he was elected provincial deputy in Katanga Province and then on 12 June as senator on a non-customary, FEDEKA ticket. Kalonji dropped the former office to hold the latter. Prime Minister Patrice Lumumba nominated him as State Commissioner for Kasaï Province in the first government of the independent Congo. The Senate rejected all of Lumumba's nominees for state commissioner on the grounds that the provincial governments had not been adequately consulted on the selections. As the country fell into crisis, Kalonji's position in national politics became tenuous due to his mixed ethnicity and the fact that he adhered to Lumumba's beliefs. He was opposed to the Katangese secession. In October he was made a member of a commission assembled by Lumumba (then deposed) tasked with managing his relations with the United Nations Operation in the Congo.