The tree is large and very hardy–to zone 4, perhaps even zone 3. It is upright, with long, curved branches and dense foliage. It is somewhat slow to bear–about four years on dwarfing stock and up to ten years on standard–and will overcrop once it becomes productive; thinning is necessary to avoid biennialism. Northern Spy is immune to wooly apple aphid, slightly resistant to fireblight, but otherwise susceptible to major apple diseases and bitter pit. The natural vigor of the tree tends to see it through however. Care should be taken when choosing a pollenizer as Northern Spy has a late bloom time.

Large, round, and often slightly flattened, the greenish-yellow fruit is striped and flushed with a delicate bloom of pinkish red. The yellowish flesh is fine grained, rather firm, very tender, crisp, and juicy. The intensely tart, aromatic, and acidic flavor is balanced with syrupy sweetness. Northern Spy is an excellent all-purpose apple, except it does not dry well. It ferments into a crisp, clean cider that is described as "distinctively minerally, almost salty, and well balanced."

The original tree grew in East Bloomfield, NY around 1800, and a plaque marks the site today. It has been claimed that the name "Northern Spy" came from a dime-store novel, The Northern Spy, which was concerned with the adventures of an abolitionist hero who posed as a slave catcher in order to hunt and kill true slave catchers.