"Codeshare agreement with Vistara opens up more than 20 destinations across India for United Airlines," Vistara said in a statement.
"Ticket sales by the agreement will begin later this year, pending government approvals," it added.
Full-service carrier Vistara has got the permission from the central government to operate international flights. However, it has not started international operations yet.
"The agreement enables United Airlines to codeshare on Vistara-operated Indian domestic flights and allows for customers of both carriers to earn and redeem frequent flier miles," Vistara said in the statement.