Catt will leave his role as attack coach at his Premiership employers to take up a position with the Red Rose ahead of the June tour.
The former England international's appointment was confirmed after World Cup-winning New Zealand coach Wayne Smith turned down the opportunity to join Lancaster's backroom team.
Smith insisted his decision was purely down to family reasons but after shaking off the disappointment, Lancaster - who led England to four RBS 6 Nations victories - expects Catt to prove his worth.
"Mike will clearly bring a lot to the attacking game but equally I will be expecting him to manage our exit sets, our kicking strategy, our organisation of set-piece defence," said Lancaster.
"I am sure he's more than capable of doing that.
"Mike has played at the top level and is highly respected.
"He has done a great job whilst coaching at London Irish and we are looking forward to working with him on this South Africa tour.
"Mike's experienced in playing in South Africa and this will be invaluable."