The weekly mass participation Parkrun events are set to resume in England by the end of October.
Parkrun events were suspended worldwide in March because of the global coronavirus pandemic.
Events will operate within Parkrun's government-approved Covid-19 framework, though there have been "minimal changes" to its operating model.
Parkrun said it was a "watershed moment to drive change" in creating a "healthier and happier planet".
Parkrun's chief executive Nick Pearson said they "are not able to commit to the same timeline across the other Home Nations" due to current restrictions across Wales, Scotland, and Northern Ireland.
"However, we are aware of the implications of only opening in England and are continuing our work to overcome the challenges that this presents," he added.
The Parkrun movement was founded in Bushy Park, London in 2002 by Paul Sinton-Hewitt and is now in 22 countries.
Runners or walkers can take part in 5km events on Saturday mornings while 2km junior events take place on Sunday mornings. Events are free and are run by volunteers.
There are 729 different locations across the UK staging the weekly events and more than two million runners have taken part.
Pearson added: "Everything in life comes with a risk, and we know and accept that we cannot remove all risks from the Parkrun environment. However, it is also important to balance the public health benefits of reopening our events, against the associated public health risks.
"We now believe, having spent considerable time gathering and understanding the evidence, that the benefits to reopening Parkrun far outweigh the risks."