Chelsea will pay around €25m plus bonuses for the 28-year-old, according to Marca, comfortably making Chavarria the most expensive departure in Rayo Vallecano's history.
He is reportedly already in London, with the move expected to be confirmed within hours once the final paperwork is completed. The signing addresses the gap left by Marc Cucurella's move to Real Madrid earlier this summer, with head coach Xabi Alonso having personally pushed for Chavarria as his preferred replacement.
Chavarria made 125 appearances for Rayo, contributing two goals and eight assists, and only established himself in La Liga relatively late, not making his top-flight debut until he was 24. It was current Liverpool manager Andoni Iraola who brought him to Rayo from Real Zaragoza in 2022, and he went on to become one of the division's most reliable full-backs, helping keep nine clean sheets last season alone while also contributing at the other end of the pitch.
Rayo had been adamant they would only sell for a fee close to Chavarria's release clause, and had already turned down an initial offer from Chelsea worth around €15m before the two clubs found common ground.
The move represents a significant financial statement from a club known for punching above its weight in Spain's top flight, and gives Chelsea a specialist left-back with Champions League ambitions after Alonso made clear he wanted an experienced, combative option to compete for the position.
Chavarria's rise has been unusually late by modern standards: his first taste of European football did not come until he was 27, when he was sent off on his Conference League debut against Swedish side Hacken.
That slow-burn trajectory has only added to the appeal for Alonso, who is understood to value Chavarria's mentality as much as his technical attributes, and who was promised significant say over incoming transfers when he took the Chelsea job.