The YouTuber, 25, publicly raised the stakes after Matchroom boss Hearn refused to get a tattoo in the event of Taylor losing.
Serrano, 33, has an impressive 42-1-1 boxing record and takes on Irish ring legend Taylor, 35, in her next fight on April 30.
And the proud Puerto Rican has the full support of her upstart promoter, who has vowed to put his money where his mouth is.
Paul also pledged to give Serrano his entire winnings if she wins.
Hearn said: “You’re fully confident that your charge will be victorious and become undisputed lightweight world champion?”
Paul said: “More confident than you are.”
Hearn added: “Really? I don’t think so.”
WATCH: Jake Paul has bet Eddie Hearn $1 million that Amanda Serrano will beat Katie Taylor
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Paul added: “I’ve got a bet for you Eddie.”
And Hearn said: “I’m not getting a tattoo.”
Paul replied: “I’ll bet you all the jewellery that I’m wearing right now that Amanda will win the fight.”
Hearn remarked: “I was hoping to bet for a lot more than that.”
Paul continued: “Well let’s put it on.”
Hearn joked: “I mean, 10 grand’s not a lot.”
Paul interjected: “This is 500k. 500k.”
Hearn continued: “We’ll talk. We can have a bet. Me and you can have a bet.”
Paul pointed out: “Well I just proposed it. 500k. [I’m] dripping right now.
Hearn replied: “Okay well maybe we can talk about a million but we’ll have a chat.”
Paul insisted: “Let’s do a million.”
Hearn revealed: “Okay. We’ll talk. I know about your bets.”
Paul pledged: “I bet Amanda wins for a million dollars.”
Hearn answered: “Okay, we’ll get it together, don’t worry. Actually we’re the underdogs in the fight apparently with the bookmakers.”
Paul proposed: “Come on. I’ll meet the oddsmakers’ odds too. A million plus odds.”
Hearn pointed out: “You don’t need to, you’re the favourite.”
Paul persisted: “Regardless, let’s do it. Let’s shake up on it. Let’s go.”
The pair then shook hands to seal the deal much to the delight of those in attendance.
Hearn said: “Anyway we’ll get that papered up because I’m not sure about you.”
And Paul said: “One million dollar bet – let’s go!”