Barclays is moving €190bn (£166bn) of assets to Dublin because it "cannot wait any longer" to implement its Brexit contingency plan.
The High Court, which has approved the move, says the move involves 5,000 clients. However, few jobs in London are expected to be affected.
The business amounts to around 15% of the bank's £1.2 trillion in total assets and was previously conducted in the UK through branches across the EU.
The plans will be in place by 29 March.
The bank's Dublin operation is expected to double in size to 300 people as a result of the business being channelled though the Irish capital.
"As we announced in 2017, Barclays will use our existing licensed EU-based bank subsidiary to continue to serve our clients within the EU beyond 29 March 2019, regardless of the outcome of Brexit," the bank said.
"Our preparations are well-advanced and we expect to be fully operational by 29 March 2019," it added.
The bank had to ask the High Court for approval to transfer the business which took place in branches in Germany, France, Spain, Italy, the Netherlands, Portugal and Sweden for corporate banking, investment banking and some wealthy private clients.
The judgement from Mr Justice Snowden said: "Due to the continuing uncertainty over whether there might be a no-deal Brexit, the Barclays group has determined that it cannot wait any longer to implement the scheme".
The scheme is based on a "no-deal" Brexit, the judgement said. This envisages the parts of the bank's business which is affected losing their "passporting" rights which currently allow them to conduct investment services activities in the remaining 27 EU member states.
"The design of the scheme has been based upon an assumption that there will be no favourable outcome of the current political negotiations between the UK and the EU as regards passporting or the grant of equivalence status to the UK in respect of financial services," the judgement said.