Historians likely will recall July 2024 as the moment that forever changed television. That was the month YouTube broke not one but two Nielsen viewership records: It became the first streaming service to account for more than 10% of total TV viewing time as well as the first to surpass the sum totals of major media distributors like Disney and Paramount.

YouTube’s viewership — in living room TVs, not just on phones or laptops — has been growing steadily. But 2024 was a breakthrough year for the 19-year-old Alphabet-owned platform. In October, YouTube accounted for 10.6% of all TV viewership compared to Netflix’s 7.5%, according to Nielsen’s Gauge report, which measures the most-watched streamers each month. That was up from December of 2022, when the platform hit 6% compared to Netflix’s 7%.

YouTube also ranked No. 1 on Nielsen’s Media Distributor Gauge Report, which measures the most-watched media distributors on a monthly basis. During the...