Raza Laskar, 32, of Ashton-under-Lyne, Greater Manchester, pleaded guilty to charges including sexual activity with a child and making indecent images of a child at Manchester Minshull Street Crown Court.
Detectives raided Lasker's home after more than 1,600 files containing indecent images of children were placed on a file sharing site between Christmas Day last year and 27 January 27, and the IP address of the device they were uploaded from was traced to Laskar. More than 1.2 million indecent images and videos of Laskar engaged in sex acts with children in a hotel room were found on computers and data storage devices after the 2 May raid.
Laskar, who is married, was caught as part of a nationwide sting called Operation Notarsie, which targeted users of the dark net, an encrypted internet network, as well as other areas of the internet not accessible through search engines.
More than 650 suspected paedophiles, including, doctors, teachers and former police officers have been arrested as part of the operation, the biggest of its kind in more than 10 years.
Laskar will be sentenced on 9 January.
