Blues boss Andre Villas-Boas confirmed the news at a press conference in Bangkok, although 19-year-old Romeu is yet to have a medical or agree personal terms as he is currently with Spain preparing for the FIFA U20 World Cup in Colombia.
Romeu made his debut for the Barcelona first team at the end of last season, but is not part of Pep Guardiola's long-term plans at the Nou Camp.
A statement on the Chelsea website read: "Chelsea Football Club has agreed terms with Barcelona for the transfer of Oriol Romeu."
Romeu could help fill the void left by the serious knee injury suffered by Michael Essien earlier this month.
Villas-Boas said: "It is a part of the squad in which we are struggling with numbers because of Michael Essien's injury and Oriol is a player with a bright future. He still has to evolve as a player.
"The Barcelona B team had a magnificent year in the Spanish second division - they finished third.
"Oriol had an injury during the season but he came back late on and was in time to play for the first team.
"So he is one of the most promising young players in that position and hopefully we can agree personal terms and hopefully he will pass a medical."
Villas-Boas also revealed the decision to loan Belgian goalkeeper Thibaut Courtois to Atletico Madrid once he completes his move from Racing Genk had not been finalised.
"The Spanish League is an extremely competitive league and Atletico is a great club to be at but it is not decided yet on his future," Villas-Boas said.
"It is still a couple of days until we can confirm agreement between all three parties."
Villas-Boas' is likely to spend again before the transfer window closes, with the blessing of chief executive Ron Gourlay.
Chelsea have seen two bids for Tottenham playmaker Luka Modric rejected this summer and are reportedly preparing a third and final offer in the region of ?35million.
They are also said to have made an offer of up to ?18million for Anderlecht wonderkid Romelu Lukaku.
Gourlay said: "From our activity in the marketplace in the past, if the coach feels there is a player available that can strengthen our team then we almost definitely go into the market place."
Source: Team Talk
Source: Team Talk