Launched in September 2018, the service is required to play most Switch games online (Fortnite is a notable exclusion).
Members can also access a growing library of classic NES games, back up save data online, and receive special offers including free access to Tetris 99.
“Global memberships now exceed 9.8 million accounts, excluding free trial memberships,” Nintendo president Shuntaro Furukawa said during a recent financial results briefing.
The figure includes family memberships, which offer up to eight Nintendo account holders access to the service under a single plan.
It represents a significant portion of the console’s user base — Nintendo says lifetime Switch sales total 34.74 million units.
Furukawa also said Tetris 99 “has been played by 2.8 million accounts” since its release in February.
Individual Nintendo Switch Online memberships cost $3.99/£3.49/€3.99 for one month, $7.99/£6.99/€7.99 for three months, and $19.99/£17.99/€19.99 for 12 months, while annual family memberships cost $34.99/£31.49/€34.99.
Twitch Prime account holders can currently get up to 12 months of Nintendo Switch Online membership free.
For the business year ended March 31, digital revenue from Switch software sales and Nintendo Switch Online memberships almost doubled to ¥118.8 billion ($1.1 billion/£825,000).