Jules Stenson, 48, entered his guilty plea at a case management hearing at the Old Bailey court here.
His plea follows an investigation by Operation Pinetree - the police inquiry into the features desk at the paper.
Former deputy editor Neil Wallis appeared beside Stenson and pleaded not guilty to the same offence.
Wallis is expected to go on trial next June.
Stenson admitted conspiring to intercept voicemail messages at the now defunct Sunday tabloid newspaper between January 2003 and January 2007.
Brooks was found not guilty of phone-hacking charges.
Reporter Dan Evans, who admitted phone hacking, gave evidence during their trial that Stenson employed him specifically to do "stuff with phones".
Earlier in July, Coulson was sentenced to 18 months in jail for his involvement in the phone-hacking scandal that rocked Rupert Murdoch owned newspaper.
Members of the British royal family, celebrities and crime victims were among some of the victims of hacking at the newspaper.
