Louis Oosthuizen fired a 6-under 66 to get within three strokes of the winner. He finished at 12-under-par 276. Keith Horne shot a closing 68 to take third place at 8-under-par 280, with Alan McLean finishing one stroke further back at minus-7.
McLardy opened the day with a seven-shot cushion and was never seriously challenged. The South African got his round going at Leopard Creek with a birdie at the par-5 second for the fourth straight round.
He cruised to seven straight pars before stumbling to a bogey at the 10th. The par-5 15th yielded its fourth birdie in four days to McLardy, which moved him to minus-16.
The 30-year-old, who won the Nashua Masters two weeks ago, stumbled to a bogey on No. 17, but he closed with a par for the easy win.
'I achieved that early in my career and then lost them both, so my confidence took a big whack,' said McLardy of losing his playing privileges on both the European and United States PGA Tours. 'I thought I couldn't compete at that level. But hopefully with a bit more experience and being a bit older we can get there again and stay there.'
The win secures McLardy a spot in the WGC-NEC Invitational field, as well as a spot in the fields at the dunhill links championship and the WGC-American Express Championship.
Desvonde Botes, who shared second place entering the round, stumbled to a 2-over 74. He shared fifth place with Nic Henning, who posted a final-round 70, at 6-under-par 282.
Marc Cayeux, James Kingston, Craig Lile, Thomas Aiken and Barry Painting shared seventh place one stroke further back at minus-5.
Ashleigh Simon, the first woman to play in a men's event in South African Tour history, closed with a 7-over 79 to finish 10 strokes worse than her nearest competitor. She finished at 28-over-par 316.