University of Oxford scientists are recruiting 18-55-year-olds for the trial in the Thames Valley region.
The vaccine is already in production but will not be ready for a number of weeks.
The trial will provide information on the safety aspects of the vaccine, as well as its ability to generate an immune response against the virus.
Participants are not expected to receive the vaccine for some weeks, and in the meantime preclinical work is being done and the vaccine is being manufactured to clinical grade standard at the Clinical Biomanufacturing Facility at Oxford University.
The trial has been approved by UK regulators and ethical reviewers.
Scientists are working as quickly as possible to get the vaccine trial ready, which includes further preclinical investigations and production of a larger number of doses of the vaccine.
Professor Adrian Hill, director of the Jenner Institute at the University of Oxford, said: "The Oxford team had exceptional experience of a rapid vaccine response, such as to the Ebola outbreak in West Africa in 2014.
"This is an even greater challenge.
"Vaccines are being designed from scratch and progressed at an unprecedented rate.
"The upcoming trial will be critical for assessing the feasibility of vaccination against Covid-19 and could lead to early deployment."
At the same time as conducting the first clinical trial, production of the vaccine is being scaled up ready for larger trials, and potentially, future deployment as soon as possible.
Dr Sandy Douglas, who is leading on the vaccine manufacturing scale-up project, said: "The scale of this epidemic poses a huge challenge for vaccine manufacturing.
"We need to follow rigorous safety standards and that takes time.
"By starting work on large-scale manufacturing immediately, we hope to accelerate the availability of a high-quality, safe vaccine."
The particular vaccine being tested was chosen because it can generate a strong immune response from one dose and it is not a replicating virus, so it cannot cause an ongoing infection in the vaccinated individual.
This also makes it safer to give to children, the elderly and anyone with a pre-existing condition such as diabetes.
People interested in volunteering can find more information on the Covid-19 vaccine website.