Aranburu has raced with Spanish teams throughout his career so far, starting out with Euskadi-Murias in 2016 and then spending the last three seasons at Pamplona-based Caja Rural.
He has three career wins to his name, including stages at the Vuelta a Madrid and Vuelta a Burgos this season.
He also took the points jersey in Burgos, weeks after finishing second in the Circuito de Getxo – a race he won last year.
Aranburu is currently nearing the end of his second participation at the Vuelta a España, where he has runner-up on two stages so far. He was beaten by Nikias Arndt in a sprint in Igualada on stage 8 and finished just behind Philippe Gilbert in Bilbao on stage 12.
"I think Astana Pro Team has proven to be one of the best teams in professional cycling and I’m very happy to join this amazing squad for the next two seasons," Aranburu said.
"This team showed that they can challenge and develop riders to make the next step in their careers, so I’m glad I can now experience this myself. I am happy to do my own big step in the WorldTour with Astana!"
Aranburu will form part of a sizeable Basque contingent at the Kazakh squad, joining up with two-time Vuelta KOM winner Omar Fraile as well as Ion and Gorka Izagirre. Fellow Basque rider and double Giro d'Italia stage winner Pello Bilbao has yet to confirm his 2020 destination, though has been linked with Bahrain-Merida.
The signing of Aranburu continues the long links between the team and Spain, with Astana having started out as a phoenix team after the demise of Liberty Seguros in 2006. Since then, the likes of Alberto Contador, Mikel Landa and, among the current crop, Luis León Sánchez, have raced for the team.
Aranburu's addition gives Astana a punchy rider who can put in a good sprint – at Burgos he won a tough uphill sprint and finished second to Giacomo Nizzolo on a less steep finish.
"Alex Aranburu is an interesting rider who can perform well on almost every terrain," said team manager Alexander Vinokourov of his new signing. "He has a good sprint and he is able to perform on hilly and mountain courses.
"He already showed some strong results at the Pro Continental level, so it will be interesting to see his progress in the WorldTour being part of our team. I think that Aranburu will strengthen our squad in stage races and Grand Tours. He’s impressing us at La Vuelta this year, so I expect we’ll see more from him in the upcoming seasons."
Astana have been actively seeking out younger riders this off-season, with Aranburu joining 23-year-old Aleksandr Vlasov (from Gazprom-RusVelo), 21-year-old Vadim Pronskiy (Vino-Astana Motors), 22-year-old Harold Tejada (Medellín) and 26-year-old Davide Martinelli (Deceuninck-QuickStep) already confirmed for 2020.
Italian trio Davide Ballerini, Davide Villella and Dario Cataldo are on the outgoing list, Ballerini to Deceuninck-QuickStep and the latter two to Movistar. Magnus Cort (EF Education First), Andrey Zeits (Mitchelton-Scott) and Jan Hirt (CCC Team) are also leaving the team.