"From today on, I will work as a manager responsible for the group's external relations and the development of new business areas," writes 47-year-old Szijjártó on Facebook.
He clarifies that he is also leaving his parliamentary seat, which he has held since 2002.
In recent years, BYD has - while Szijjártó was in government - made Hungary its European hub with the help of substantial financial support from the Hungarian state.
The country's new Prime Minister Péter Magyar has said that Szijjártó "has long represented foreign interests," and Magyar now writes on Facebook:
“The only difference from before is that from now on, Péter Szijjártó will not be paid by the Hungarian people for the same ‘work’, but by his actual employer.”
