The station is on a raised viaduct running in a roughly north-south direction. There are two exits, the north exit (北口?) and south exit (南口?). Both exits have ticket vending machines and toilets; however, the north exit has a Midori no Madoguchi staffed ticket office and escalators to the platforms. Luggage lockers are available at the south exit.
The station has two island platforms with two tracks on either side of each platform. Platforms 1 and 4 (the outermost tracks) serve the Keihin-Tohoku Line, while platforms 2 and 3 (the inner tracks) are used for Yamanote Line trains. This platform arrangement allows for easy cross-platform interchanges so that passengers may transfer between lines in the same direction by walking across the platform. East of the platforms lie tracks belonging to the Tohoku Main Line formerly running to Tokyo Station but which are now used to stable trains terminating at Ueno Station.
In fiscal 2013, the station was used by an average of 67,593 passengers daily (boarding passengers only), making it the 64th-busiest station operated by JR East. The daily average passenger figures (boarding passengers only) in previous years are as shown below.
Okachimachi Station is in the centre of a busy commercial district stretching southwards from Ueno Station. Particularly well-known is Ameya-Yokochō ("Ameyoko"), a busy shopping street dominated by small market-style stalls selling a wide variety of wares. Ameyoko runs parallel to the railway line and includes a large market under the railway tracks.