The 拢31m deal was first announced in May 2004 but comes amid a massive sell-off of strategic assets by the broadcasting giant.
The remaining 25% of the company remains in control of the Walt Disney Company, though ITV is now obliged to offer the company the same terms for its share of the business.
Charles Allen, chief executive of ITV, said: 鈥淕MTV is an excellent business and in 2003 grew its share of viewing.
鈥淚TV Plc鈥檚 acquisition of an increased stake in GMTV at a fair price has simplified the ownership structure and will enable ITV and GMTV to work even more closely together."
The GMTV brand is the highest-rated breakfast period output in the UK and has cemented its position since the demise of Channel 4鈥檚 Big Breakfast and the ill-fated RI:SE.