The government said it will deport migrants to Rwanda in two weeks on 14 June.
The Home Office said it had begun issuing formal removal notices to migrants as the "final administrative step" in its partnership with the east African nation.
The home secretary said that there would still be attempts to delay the process.
Priti Patel said: "Our world-leading partnership with Rwanda is a key part of our strategy to overhaul the broken asylum system and break the evil people-smugglers' business model.
"Today's announcement is another critical step towards delivering that partnership and, while we know attempts will now be made to frustrate the process and delay removals, I will not be deterred and remain fully committed to delivering what the British public expect."
The Home Office said an initial group of migrants had started to receive formal letters telling them they are being sent to Rwanda to "rebuild their lives in safety".
It said the policy is designed to break people-smuggling networks and stem the flow of migrants across the Channel.
The Home Office did not say how many asylum seekers would be on the first deportation flight to Rwanda.
Earlier this month it said it started issuing "notices of intent" to some individuals informing them they were "in scope for relocation".
It said officials are working to ensure individuals are given the "appropriate support" ahead of departure.
The government has said those sent to Rwanda will be given support, including up to five years of training to help with integration, accommodation, and healthcare.
Shadow home secretary Yvette Cooper said: "The Rwanda scheme isn't about deterring the criminal gangs or small boat crossings, it's about chasing headlines regardless of reality.
"This is a completely unworkable, extortionately expensive, and deeply un-British policy. There is no proper process for identifying people who have been trafficked or tortured.
"More than six weeks after it was announced the Home Office still hasn't said how much it will cost per person on top of the substantial £120m already spent.
"Meanwhile, there is still nothing to turnaround the huge drop in Home Office asylum decision making or to tackle the criminal gangs."
The plan, announced in April, has drawn criticism from MPs inside and outside the Tory party as well as from many charities.
UN officials have said the move would violate the international Refugee Convention.
Last year more than 28,000 migrants and refugees crossed from mainland Europe to the UK, mostly in small boats.