BOGOTÁ, Colombia—In polling stations from Venezuela to the U.S. to Europe, Venezuela’s opposition put on a primary election Sunday in which a conservative, pro-business engineer was expected to be chosen as the candidate to challenge authoritarian President Nicolás Maduro’s regime in next year’s presidential election. 

Maria Corina Machado held a commanding lead in polls, and her victory was foretold in a field of 10 candidates. But as of early Sunday night, it remained unclear if she would be permitted to run in the general election because Maduro’s government has barred her, as it has other prominent dissident politicians, from holding office.