Allison returned to front-line duty last year as part of a job swap with Mike Elliott, who wanted to step away from the technical director position and originally moved into the chief technology officer position before leaving the squad at the end the season.
While at the time it was unclear how long Allison would want to stay in the role, having originally joined Mercedes in 2017, his rekindled enthusiasm for F1 has now resulted in him signing up for the long haul.
