The scheme launches on Wednesday 1 December and will run until 17 December.
However, only those who are signed up to the Costa Club app before the start date will be eligible to get their hands on the free goodies.
Winners will have four weeks to claim their hot or cold Costa drink, which can be customised by size, number of shots and type of syrup.
The giveaway also includes all of Costa's "handcrafted" coffees, teas, fruit coolers and Frostino frappes.
How do I claim my free drink?
Those who are signed up to the app ahead of 1 December will be eligible to claim the free drinks up until 17 December.
To claim the offer, simply check the rewards section in the app and the free drink voucher should appear.
The voucher can be redeemed in store or when ordering online using click and collect.
A Costa Coffee spokesperson said: "As the season for giving approaches, we’re excited to announce our one million free drinks giveaway via our Costa Club app in the hope that we can encourage our members to make someone’s day with a simple, but kind gesture of a cup of their favourite coffee.
"We also hope our one million free drink giveaway sparks not only a bit of joy but also encourages precious conversations and the great feeling making someone else’s day a bit brighter.”
Currently, Costa Club app members earn one bean for every drink they purchase.
Once eight beans have been collected, members will then receive a voucher to claim any barista-crafted drink for free.
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