Mehdi El Ghaly from Morocco was going to be one of the official artists in residence at the event, which starts this weekend.
But the Home Office has barred him from enterting the country.
Festival artistic director Adrian Turpin is calling on Scottish Secretary David Mundell to help overturn the decision and has also written to Dumfries and Galloway MP Alister Jack for help.
He said: “It is disappointing and frustrating that a respected young storyteller involved in a long-running arts project designed to bring people together should be denied a visa to attend an international festival.
“Wigtown Book Festival involves writers, journalists, academics, artists and visitors from all over the world and is an award-winning showcase for Dumfries and Galloway, Scotland and the whole of the UK.
“We are calling on the region’s MPs and MSPs to make representations to the Home Office, whose decision mars the country’s reputation for intellectual openness and exchange.”
Mehdi and photographer Houssain Belabbes, pictured above, have been working with Scottish counterparts Anne Errington and Laura Hudson Mackay on a project called Confluence exploring and comparing storytelling traditions from the two countries.
The duo have been awarded a fully funded residency at the festival where they were due to tell stories, many illustrated by photography and work with festivalgoers to gather or create new tales.
The project was planned as an exchange, the second part of which would see the Scots welcomed to Morocco.
Criticising the visa ban, Laura said: “To deny a gifted, enthusiastic young man who wants to share his storytelling talent and culture with us in Scotland is shortsighted and negative.”
She vowed that Confluence will continue, however, and plans to travel to Marrakech in October to share it over there too.