Newcastle Knights have appointed Sydney Roosters assistant Adam O'Brien as their coach for next season following Nathan Brown's departure.

Brown left the Knights on Tuesday after a 46-4 defeat to Wests Tigers, with the NRL club having announced the coach would leave at the end of the 2019 campaign the previous week.

The Knights have moved quickly to bring in a replacement, with O'Brien agreeing a three-year contract which will run from 2020. 

O'Brien joined the Roosters - where he will remain until the end of their NRL finals campaign as they aim to defend their crown - last year after spending 11 seasons with Melbourne Storm.

Kristian Woolf will take temporary charge of the Knights, who cannot make the finals and face Penrith Panthers in their last match of the season.

"We are very excited to have Adam coming in as head coach," Knights chief executive Philip Gardner told the club's website.

"Aside from quality coaching, we want quality people within the organisation and Adam ticks all of those boxes."

O'Brien said: "The Knights are a strong club with a significant and passionate supporter base.

"I have been patient throughout my coaching career, but the time is right to make this move and all of these attributes made the move to Newcastle an easy decision.

"I am excited about what is around the corner, but my sole focus over the next five weeks remains with the Roosters and our finals campaign. That isn't something I take lightly.

"Once the 2019 season has concluded, I will turn my attention to Newcastle."