More than 32,000 volunteers took part, mostly in the US, but also in Chile and Peru.
The vaccine was 79% effective against stopping symptomatic Covid disease and 100% effective at preventing people from falling seriously ill.
And there were no safety issues regarding blood clots.
That should further reassure some EU countries that recently paused rollout of the vaccine amid concerns about a possible link.
Some are already starting to use it again now that Europe's medicines regulator has completed its review and has also concluded the vaccine is safe and effective.
This new trial data may also prove useful in reassuring people about how well the vaccine works to protect the elderly against Covid-19 illness.
Several countries initially would not authorise the use of the vaccine in adults over 65, citing lack of evidence.
Around a fifth of the volunteers in this trial were over 65 and the vaccine - given as two doses, four weeks apart - provided as much protection to them as to younger age groups.
Hundreds of thousands of people in the UK are already receiving the AstraZeneca vaccine every day, so these numbers are tiny by comparison.
But the results are vital for the US and should clear the way for the vaccine to be approved by regulators there within the next month or two.
Lead investigator of the Oxford University trial of the vaccine, Prof Andrew Pollard said: "'These results are great news as they show the remarkable efficacy of the vaccine in a new population and are consistent with the results from Oxford-led trials.
"We can expect strong impact against Covid-19 across all ages and for people of all different backgrounds from widespread use of the vaccine."
Prof Sarah Gilbert, co-designer of the vaccine, said: "In many different countries and across age groups, the vaccine is providing a high level of protection against Covid-19 and we hope this will lead to even more widespread use of the vaccine in the global attempts to bring the pandemic to an end."
Prof Gilbert said there were always cases of people falling ill after receiving a vaccine, particularly when very large numbers of were receiving a jab, but that did not mean that the vaccine was responsible for the problems. Meanwhile thousands of people a day were now dying across Europe from Covid-19.
She said: "It is really important that we get the chance to protect people as quickly as possible. This vaccine will save lives."