Jodie Whittaker (Beth Latimer), Andrew Buchan (Mark Latimer) and Arthur Darvill (Rev. Paul Coates) are also confirmed for the next run.
Tennant (DI Alec Hardy) previously signed up to star in Gracepoint - a US remake of Broadchurch - calling into question his continued participation with the original show.
However, it has now been confirmed that the Scottish actor will appear concurrently in both the UK and US versions of the series.
"We're delighted Broadchurch is back in production, but we're remaining tight-lipped about how the story develops," said ITV's director of drama, Steve November.
"Suffice to say Chris [Chibnall] has delivered as always and the scripts are just as exciting as the first series."
Broadchurch will resume filming in Dorset soon, with the remainder of series two's cast to be announced in the near future.