Saints have moved quickly to replace Sean Long by appointing former Halifax boss Richard Marshall as assistant coach on a deal running until the end of the 2020 season.
Long left the club earlier this week to take up a position at Harlequins RU with immediate effect.
Marshall, 43, has earned praise as one of the sport’s most promising coaches after taking part-timers Halifax to three top-four finishes in his four seasons at The Shay, as well as developing a number of home-grown talents.
Marshall has worked in Super League before, having been an assistant to Tony Smith at Warrington Wolves, and now brings his experience to the Super League leaders to work along side Holbrook.
Marshall said of his new role: “I had a number of options after I left Halifax, but I met Mike Rush (Saints' chief executive) and Justin and when a club like this comes calling, you jump at the chance.
“This is a wonderful opportunity to continue my development at a fantastic club and I cannot wait to get started.”
Holbrook said:“It’s great news for our club that Richard has decided to join us .
''He had a few offers and opportunities he could have taken up elsewhere, but he has chosen our club which is a great sign of the direction we are going and it is great to have such an experienced coach join us.
''Richard has proven himself as a great assistant early in his career at Warrington and has obviously done a fantastic job at Halifax over the last four and a half years so I am looking forward to working with him.”
Rush said: “We all welcome Richard to the club with open arms. I have known him for more than 15 years and watched him rise through the ranks at Warrington and more recently at Halifax.
“He absolutely fits the culture of the club. He is hard-working, driven and a talented individual who will bring further experience to our coaching staff.”
As a player, Marshall represented Ireland and played at club level for Halifax RLFC, Huddersfield Giants, London Broncos and Leigh RLFC, as a prop or second-row between 1995 and 2007.
He will will start his new role with immediate effect and will be alongside Holbrook and fellow assistants, Paul Wellens and Ian Talbot, for the visit of Huddersfield Giants to the Totally Wicked Stadium on Friday.