The adverts are only for the free tier, and users will see up to two minutes of ads while waiting in queue to start a gaming session.
Nvidia spokesperson Stephenie Ngo said that the free tier often means waiting in line for a remote computer to free up before every hour of free gameplay - now, there'll be a few ads while you wait.
Nvidia says the ads should help pay for the free service tier, and it hopes the change "will cut average wait times for free users over time."
However, GeForce Now's free tier has never been its queues. Rather, it's the worst version of the company's service and doesn't show what cloud gaming can do.
The only way for users to experience cloud gaming is to try GeForce Now Ultimate, which gives you the power of an RTX 4080 in the cloud, much lower lag, and now G-Sync monitor support. But it still costs £14.50 a month, with no free trial.
The company plans to email all free-tier users to tell them about the ads.
In October, Nvidia hiked the price of GeForce Now in countries other than the US. Nvidia said the hikes "account for higher running costs" in the countries where they rolled out. In recent months, many streaming services have had price hikes and added ad-supported tiers.