The R&A has confirmed that all existing exemptions achieved for the event before it was cancelled in July due to the Covid-19 pandemic are being honoured next summer.
That means MacIntyre will be in the field at the Kent venue on 15-18 July on the strength of his top-10 finish behind Shane Lowry in the 2019 event at Royal Portrush.
Others to secure spots include Aberdeen Standard Investments Scottish Open champion Aaron Rai, who gets in through a top-10 finish in the Race to Dubai.
The remaining 50 places will now be determined by updated exemption categories, which include players inside the top 50 in the world rankings on 23 May 2021.
A minimum of eight spots will also be available at Final Qualifying on 29 June.
Johnnie Cole-Hamilton, executive director – championships at The R&A said: “We believe that it is important to honour all of the exemptions that were confirmed before The 149th Open was cancelled this year and so we are in a unique situation where a large number of players have already qualified and are in the field.
“In light of these exceptional circumstances, we have carefully reviewed our exemption categories and made adjustments so that players can earn places in the Championship from results achieved in both the 2020 and 2021 seasons as well as retaining opportunities through our qualifying events.”
Qualifying places will no longer be offered at the remaining events originally scheduled as part of The Open Qualifying Series for 2020.