FC Cincinnati will join MLS in 2019 after being granted an expansion franchise, the league announced on Tuesday.

Already competing in the United Soccer League – the country's second-tier competition – Cincinnati will begin playing next season ahead of the planned opening of a new 21,000-seat stadium in 2021.

Cincinnati have been a sensation in their three years in existence, with a better average attendance than some MLS teams from the very beginning.

Those numbers are at an all-time high so far in 2018, with an average of 24,417 coming out to home games at the University of Cincinnati's Nippert Stadium.

That number is more than double the next-best average in the USL and would rank fifth among MLS's 23 teams this year.

"Major League Soccer is proud to introduce Cincinnati as our 26th team," Commissioner Don Garber said. "The rise of Cincinnati as a passionate soccer market in recent years, coinciding with the city's growing economy and reputation as a top destination for young professionals makes it an ideal city for our growing league.

"We congratulate Carl Lindner and his partners, and also the soccer fans of Cincinnati, who have passionately supported FC Cincinnati in the USL."

Cincinnati's support has made the club a favourite in the current round of MLS expansion, but the city had to sweat it out as stadium details were finalised and Nashville were awarded one of two available franchises late last year, leaving Cincinnati to fend off Detroit and Sacramento for the other spot.

Now Cincinnati will join the league a year ahead of Nashville (and the long-awaited Miami team backed by David Beckham), making the transition next season.

Cincinnati will continue to play at Nippert for at least two more seasons before the planned opening of their new stadium.

MLS still plans to add two more teams in the coming years, bringing the total to 28.