Coach Steve Borthwick has kept faith in the team that outclassed Argentina 35-12 in the first test last weekend, despite the fact they are missing a host of players on tour with the British & Irish Lions in Australia.
"Saturday's match in San Juan is another great challenge," said Borthwick. "The players have trained with real focus and intensity this week, determined to keep improving in every area.
"We're expecting a tactical battle as well as a tough, physical contest, and everyone is excited for what should be a fantastic test match."
Harlequins centre Northmore, 28, will partner Seb Atkinson in the midfield, with George Ford at flyhalf and Ben Spencer in the number 10 jersey.
The back three contains wingers Will Muir and Tom Roebuck, with Freddie Steward at fullback.
Jamie George is at hooker with props Fin Baxter and Joe Heyes either side of him, and Charlie Ewels and Alex Coles make up the second row.
Tom Willis is at number eight, with Ben Curry and Sam Underhill the two flankers.
There is no change to the bench, retaining a 6-2 split between forwards and backs.
Ford and George will again act as co-captains.
After this weekend, England's summer tour concludes with a match against the United States in Washington D.C. on July 19.
England matchday squad v Argentina:
Starters: 15. Freddie Steward, 14. Tom Roebuck, 13. Luke Northmore, 12. Seb Atkinson, 11. Will Muir, 10. George Ford, 9. Ben Spencer, 8. Tom Willis, 7. Sam Underhill, 6. Ben Curry, 5. Alex Coles, 4. Charlie Ewels, 3. Joe Heyes, 2. Jamie George, 1. Fin Baxter
Replacements: 16. Theo Dan, 17. Bevan Rodd, 18. Asher Opoku-Fordjour, 19. Chandler Cunningham-South, 20. Guy Pepper, 21. Alex Dombrandt, 22. Jack van Poortvliet, 23. Cadan Murley