"Brendan, Anneme and their children are returning to South Africa in January for family reasons and, as a club very much based on family values, we respect their decision and wish them well," said Saracens chairman Nigel Wray.
"Mark and Andy will take over the day-today running of the team, but Brendan will remain an integral part of the club, as Technical Director, making freauent visits to north London.
"The direction, stability and continuity of the club are unaffected and we will continue our collective quest to be successful on and off the field, striving to win Champions in England and Europe, working hard for our players and staff, their families, our supporters and the borader community.
"We would like to thank Brendan for his outstanding contribution through the past two season, establishing a culture of honesty, discipline and work ethic that is now enshrined within the DNA of our club, and we look forward to his continuing involvement in the months and years to come.
"Equally, we are delighted to appoint Mark McCall as director of rugby, He has played a crucial role in our recent success and with his high-level experience at Ulster and Castres, is ideally equipped to maintain this progress.
"He will lead an outstanding group of coaches including, Andy Farrell, Paul Gustard, Alex Sanderson and Dan Vickers and Scott Murphy as high performance director."
Saracens face crucial back-to-back fixtures against Racing Metro 92 when the Heineken Cup returns to action in December.
The English premiership runners up lost their opening two Pool 2 encounters away to French champions Clermont Auvergne and at Wembley against former European champions Leinster.