ITV director of programmes Nigel Pickard has signed off the 12 x 90-minute order, which represents the biggest network drama commission from Scotland to date. The order will be split into two six-part series.
The long order is the second such deal that Pickard has done at ITV and follows his£200m deal last year to secure The Billfrom Talkback Thames until 2010.
The deal will come as a major fillip to Glasgow-based SMG TV Productions, which is expected to see a boost in turnover this year from£16m to£20m.
SMG TV Productions managing director Elisabeth Partyka said the commission was "a huge testament to the talent in Scotland".
The Scottish drama, which has been running for 21 years and has clocked up over 70 episodes, regularly attracted around 6 million viewers during its most recent series, which concluded earlier this month.
Production on the new series will begin in May for broadcast later this year.
The executive producer is Eric Coulter, a former producer of BBC2 drama The Copswho has been working on Taggartsince 2002.