The plan by the IBA to build a mast at the site was controversial (prompting a House of Lords debate in May 1957). This was due to its proximity to Rhoose Airport (now Cardiff International Airport, and IBA's initial plan for a 305 m (1,000 ft) mast on a site that itself is 125 m (410 ft) above sea level.
Objections were noted, the mast height was eventually limited to 229 m (750 ft) and it was built in Summer 1957 to provide 405-lineVHF television to south Wales and the west of England. Test transmissions commenced on 2 September 1957 on Band III channel 10 (199.75 MHz) from antennas at 340 m above sea level and the station entered broadcast service on that frequency in January 1958. The programming was initially provided by TWW.
The site remained on air until the closure of 405-line television in 1985.
In 1965, Band III channel 7 (184.75 MHz) was added to the mast, transmitting from an antenna array sited about 20 m below the existing channel 10 array. This was to carry the programmes of ITV's new Welsh ITV region initially provided by TWW, and from 1968 by Harlech Television (HTV Wales). From that point onwards, the channel 10 transmissions carried the programmes of ITV's new West region (again, initially provided by TWW, and from 1968 by HTV West). Channel 10's power output was decreased to 55 kW and the Wales-facing antennas were removed, though the e.r.p towards the West of England remained about the same as it had been previously.
In 1985, when 405-line TV closed, the site was re-engineered to remove the VHF television antennas. St. Hilary became just a telecommunications mast and remained so until October 2000 when Real Radio commenced FM Radio broadcasting from the site. In late 2000, DAB Digital Radio was added to the radio broadcasting repertoire initially transmitting the Cardiff & Newport multiplex on channel 11C, but with Swansea SW Wales on channel 12A commencing in February 2004.
In 2006 OFCOM received a proposal for a new Rock-Orientated FM station to transmit from the site, but nothing has come of it.