International cruises will be able to start again from England from 2 August after a 16-month break.
People arriving at UK ports who have been fully vaccinated in the US and the EU will also not have to quarantine, the UK government said.
An industry body said travel agencies, hotels, tour guides, port operators and other firms would benefit from cruises restarting.
Domestic cruises have been allowed to run from May but international cruises have been prohibited.
The government said that international cruise travel advice "will be amended to encourage travellers to understand the risks associated with cruise travel and take personal responsibility for their own safety abroad".
Richard Ballantyne, chief executive at the British Ports Association (BPA), said the domestic cruises had demonstrated how ports and cruise lines could "ensure the health and safety of passengers, crew and destinations".
He added that the BPA is "hopeful that the devolved administrations will follow suit shortly" in allowing international cruises.
The British Ports Association, which represents more than 400 ports, terminal operators and port facilities, said it was "disappointed" that arrivals from France still need to quarantine on arrival into England for ten days.
Under the new rules, from 04:00 BST on Monday 2 August, fully vaccinated travellers arriving from amber countries will not need to quarantine or take a test on day eight of their arrival.
However, they will still need to take either a pre-departure test and a PCR test on the second day after they arrive.
People will still need to complete a Passenger Locator Form.
Under-18s will be exempt from isolation, and some will not have to test, depending on their age.
The UK government said the rule changes would help to reunite family and friends whose loved ones live abroad.
Transport secretary Grant Shapps said the reopening of travel was "progress we can all enjoy".
On its website, P&O Cruises said following their UK summer staycations, its Britannia ship will begin planned western Mediterranean itineraries on 25 September, while its Iona vessel will launch on the same date.
However, it said due to the current traffic light system, a "number of itineraries have had to be cancelled".
Cruises on Ventura have been paused until 3 October 2021, while cruises on its Azura ship have been halted up until 10 December 2021. Some others have been delayed until 2022.
Paul Ludlow, P&O cruises president, has said the UK coastal cruises were "proving very popular" and added the company was "looking ahead and planning for the future with vigour".
"We are confident that destinations will soon open up their borders both for UK travellers and also for cruise ships," he said. "Spain and its islands and the Caribbean are both looking very positive and we are seeing, one by one, countries publicly looking forward to welcoming us back."
In 2019, it contributed more than $154bn (£110bn) to the global economy, according to the trade body Cruise Lines International Association, before the shops were all anchored due to the lockdown.
US giant and P&O Cruises owner Carnival, which made a profit of $3bn in 2019, reported a loss of $10bn in 2020 after its revenues plunged 73%.