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The Kiwi, dumped by Toro Rosso after his first full season as an F1 driver, will be a development driver from 2019 working in the Ferrari simulator.
Ferrari has announced is increasing its budget this year, as the Italian team looks to finally overtake major rivals Mercedes after a decade without a title.
Hartley joins Pascal Wehrlein, Antonio Fuoco and Davide Rigon as simulator operators. Hartley is also signed to Porsche as a factory driver and Formula E prospect, but had a clause allowing him to remain in a F1 role.
"Our team has taken on four undoubtedly talented drivers, who possess innate feeling, with a strong understanding of race cars and tracks," said Mattia Binotto, Ferrari team principal.
"These are exactly the qualities required in the skilful role of driving in a simulator, one of the vital pieces of equipment in Formula 1."
Wehrlein left Mercedes at the end of 2018, and races in Formula E. Fuoco rose through the Ferrari driver academy while Rigon races for a ferrari factory team.
Daniil Kvyat left the Ferrari development programme to drive for Toro Rosso.
Hartley joined Toro Rosso in late 2017, driving in four F1 races, and was retained for 2018.
Ferrari's F1 drivers are the German great Sebastian Vettel, a four-time championship winner who finished second last year, and team newcomer Charles Leclerc from Monaco.