The agreement is Ryanair’s second such deal after coming to terms with the Italian ANPAC and ANPAV unions in March.
It is the first time the airline’s cabin crew working out of its UK bases will get representation.
Some 650 staff will be covered, with the union able to fight their cause on pay, hours, conditions and holidays.
Around 25% of the Ryanair fleet operates in its UK market.
The deal comes after Ryanair last year announced it would recognise unions, and has pledged to agree more recognition arrangements in the coming weeks and months.
It initially acquiesced following a series of damaging pilot strikes, which grounded flights and forced the airline to make widespread cancellations.
However, while it has come to agreements with various pilots’ unions across Europe, including Balpa, similar negotiations over cabin crew have taken considerably more work.
The agreement will only cover cabin crew directly employed by Ryanair, not those employed via agencies such as Crewlink.
Unite currently represents around 25,000 cabin crew across airlines operating out of the UK.
Eddie Wilson, Ryanair’s chief people officer, said: “We are pleased to sign this cabin crew recognition agreement with Unite the Union in the UK. This is a further sign of the progress Ryanair is making with trade unions since our December 2017 decision to recognise them.
“We hope to announce further agreements over the coming weeks, in those countries where unions have approached these negotiations in a practical and positive manner. We are making less progress in some smaller countries where minor issues (such as days off for union officials) are unnecessarily delaying agreements.
“However, as this growing number of pilot and cabin crew recognition agreements confirms, we are making progress and confounding those sceptics who claimed that our December 2017 decision was not real or genuine.
“We look forward to working closely with both Unite the Union, and their company council to address issues of concern to our UK based cabin crew.”
The recognition agreement covers directly employed cabin crew working from Ryanair’s Belfast, Birmingham, Bristol, East Midlands, Edinburgh, Leeds Bradford, Liverpool, Stansted, Luton, Manchester and Prestwick bases.
Len McCluskey, Unite general secretary, added: “This is a historic agreement and a significant step by Ryanair. For the first time ever Ryanair’s UK cabin crew will have a recognised union in their corner to deal with workplace issues and collectively bargain on pay.
“I’d urge all UK based Ryanair cabin crew to join Unite and be part of one the biggest trade unions in the world representing airline workers. Over the coming days and weeks, Unite will be seeking similar agreements with the employment agencies which indirectly employ the remainder of Ryanair’s UK cabin crew.
“Unite looks forward to building a positive relationship with Ryanair that benefits passengers and workers alike.”