Silkworth Lodge was opened 2002 by The Families in Recovery Trust which is a Jersey registered charity and part of The Silkworth Charity Group.
The organisation offers residential rehabilitation for men and women who are affected by drug and alcohol addiction.
The partnership, which will continue up until the end of 2018, will see staff from the offshore law firm support the charity through a variety of fundraising initiatives, form dress down days to raffling off a days holiday.
The firm also entered a team into the Silkworth Extreme Team Challenge, held last week, as well as providing volunteers to help marshal the event.
Now in it's fourth year, the Silkworth Challenge is a relay style event which encompasses activities such as coasteering, cycling, running, swimming and kayaking, taking in the whole coast of the island, starting and finishing at Greve De Lecq.
Jason, chief executive officer of Silkworth Lodge, said: "We are delighted that Collas Crill has chosen Silkworth Charity Group to support as their chosen charity.
"When Collas Crill contacted me, I was really excited by the opportunity of working together, not only by us benefitting from the companies fundraising activities but also by us being able to give something back through our corporate educational & awareness programmes.
"We are all really looking forward to working with the team at Collas Crill over the next 18 months."
Collas Crill's Make A Difference (MAD) committees are based across the firm's global jurisdictions, aiming to make a positive impact on staff, the community and the environment.
Dionne Gilbert, partner at Collas Crill and head of the MAD team in Jersey, said: "It's always important to us that, as a firm, we support organisations that are making a real difference to the lives of islanders.
"We've worked with Jason and his team previously and we felt compelled to continue our support through our structured CSR programme."