Casualty's Georgia Taylor and Peep Show's Paterson Joseph join the crime drama for its seventh run.
Taylor is cast as crown prosecutor Kate Barker, while Joseph will play DI Wes Leyton.
Bradley Walsh, Paul Nicholls, Peter Davison and Dominic Rowan all reprise their roles in the new episodes.
Series seven - which features guest stars Patrick Baladi, Ramon Tikaram and Glynis Barber - opens with a two-parter from writer Emilia di Girolamo, exploring the aftermath of a devastating train crash.
Law & Order: UK returns to ITV on Sunday, July 14 at 9pm on ITV.
> Paul Nicholls quits Law & Order UK after two series