The newspaper reported that the company gave technical assistance to the NSA in carrying out a secret court order allowing wiretapping of all internet communications at the headquarters of the UN, an AT&T customer.
The documents date from 2003 to 2013 and were provided by fugitive former NSA contractor Edward Snowden, The Times reported.
The company helped the spy agency in a broad range of classified activities, the newspaper reported.
The documents describe how the NSA's working relationship with AT&T has been particularly important, enabling the agency to conduct surveillance, under various legal rules, of international and foreign-to-foreign internet communications that passed through network hubs in the US.
AT&T installed surveillance equipment in at least 17 of its US internet hubs, far more than competitor Verizon Communications, The Times reported. AT&T engineers also were the first to use new surveillance technologies invented by the NSA, The Times reported.
"This is a partnership, not a contractual relationship," according to one NSA document describing the link between the agency and the company.