Answer by taking a quote from the following article:

Patrice Emery Lumumba (alternatively styled Patrice Hemery Lumumba; 2 July 1925 - 17 January 1961) was a Congolese politician and independence leader who served as the first Prime Minister of the independent Democratic Republic of the Congo (then Republic of the Congo) from June until September 1960. He played a significant role in the transformation of the Congo from a colony of Belgium into an independent republic. Ideologically an African nationalist and Pan-Africanist, he led the Mouvement National Congolais (MNC) party from 1958 until his death. Shortly after Congolese independence in 1960, a mutiny broke out in the army, marking the beginning of the Congo Crisis.

Patrice Lumumba was born on 2 July 1925 to a farmer, Francois Tolenga Otetshima, and his wife Julienne Wamato Lomendja, in Onalua in the Katakokombe region of the Kasai province of the Belgian Congo. He was a member of the Tetela ethnic group and was born with the name Elias Okit'Asombo. His original surname means "heir of the cursed" and is derived from the Tetela words okita/okito ('heir, successor') and asombo ('cursed or bewitched people who will die quickly'). He had three brothers (Ian Clark, Emile Kalema, and Louis Onema Pene Lumumba) and one half-brother (Tolenga Jean). Raised in a Catholic family, he was educated at a Protestant primary school, a Catholic missionary school, and finally the government post office training school, where he passed the one-year course with distinction. Lumumba spoke Tetela, French, Lingala, Swahili, and Tshiluba. Outside of his regular studies, Lumumba took an interest in the Enlightenment ideals of Jean-Jacques Rousseau and Voltaire. He was also fond of Moliere and Victor Hugo. He wrote poetry, and many of his works had an anti-imperialist theme. He worked in Leopoldville and Stanleyville as a postal clerk and as a travelling beer salesman. In 1951, he married Pauline Opangu. In 1955, Lumumba became regional head of the Cercles of Stanleyville and joined the Liberal Party of Belgium, where he edited and distributed party literature. After a study tour in Belgium in 1956, he was arrested on charges of embezzlement from the post office. He was convicted and condemned one year later to twelve months' imprisonment and a fine.

What was his first job?
He worked in Leopoldville and Stanleyville as a postal clerk and as a travelling beer salesman.