Eli Mills was the personal aide and financial director for the aging Sir Benjamin Lockwood. He was an old friend of Claire Dearing from her days before Jurassic World. After the Senate opted not to intervene on Isla Nublar, Mills, under Lockwood's direction, hired mercenaries led by Ken Wheatley to rescue eleven species from the doomed island and relocate them to a sanctuary of Lockwood's choosing. Mills enlisted the aid of Claire for her knowledge of Jurassic World's dinosaur tracking system and Owen Grady so that Wheatley's men could locate and capture Blue. What no one suspected was that Mills at ulterior motives.
In reality, Mills had doublecrossed everyone. The mercenaries worked for him, not Lockwood, even though it was Lockwood who'd hired them. He'd already sent a team to the island to retrieve a DNA sample of the Indominus rex in the form of a rib bone. From this, Dr. Henry Wu was able to create the Indoraptor. With the assistance of auctioneer Gunnar Eversol, he planned to sell the "rescued" dinosaurs to the highest bidder in order to fund the experiments of Dr. Wu to create a true successor to the I. rex as the Indoraptor was not exactly everything Mills hoped it'd be.
When Lockwood's granddaughter Maisie stumbled onto Wu's lab and overheard the two men discussing this, Mills locked her in her room. He also imprisoned Owen and Claire when Wheatley captured the two having stowed away aboard the mercenaries' ship, the Arcadia, and murdered Lockwood when his employer learned of what he was doing. He framed the death as being of natural causes, naming himself as Maisie's guardian, firing housekeeper Iris Carroll who'd raised both Maisie and her mother.
The auction went ahead as planned at Lockwood's mansion until Eversol unveiled the Indoraptor. Only intended as an example of what the bidders' money would be going towards, Russian arms dealer Anton Orlov was so impressed with what he saw that he began a bidding war on the hybrid, which Mills allowed despite Wu's protests that the Indoraptor was too dangerous. Orlov won the bid, but then Owen and Claire escaped captivity and released a Stygimoloch into the auction room, causing chaos. The bidders fled.
Wheatley unintentionally let the Indoraptor loose when he entered its cage after tranquilizing it, intending to take one of its teeth for his collection, leaving the door unlocked. The hybrid, not fully tranquilized, awoke, killing Wheatley, Eversol and several bidders. Mills' attempt to recapture Owen and Claire and regain custody of Maisie was foiled when the Indoraptor intervened, killing his mercenaries, forcing him to flee.
He attempted to leave the mansion in a van with the I. rex bone until Maisie released all the caged dinosaurs, who stampeded, killing the last of Mills' mercenaries and destroying his van. Mills himself was seized and eaten by a Tyrannosaurus rex and a Carnotaurus, with the T. rex stepping on and crushing the I. rex bone.