Currently the England assistant coach, Farbrace worked with Herath in two separate stints with the Sri Lanka team. The first came as Sri Lanka's assistant coach, between 2007 and 2010. The second was in 2014, when he was briefly the head coach.
"In subcontinental conditions, Rangana's up there with Murali, Kumble and the greats," said Farbrace. "In these conditions, he knows how to get the most out of them. Where others might have up-and-down days, he stays on exactly the same path the whole time. He deserves the wickets he has got, because he's absolutely fantastic.
Farbrace, now tasked with helping prepare this England team for facing Herath, had been in the Sri Lanka dressing room when Herath was recalled to the Test side in 2009. At the time, Herath was in England, playing league cricket in Staffordshire, and did not have a stable place in the Sri Lanka side.
He made the most of that recall, however, taking 4 for 15 in the second innings of that game to bowl Sri Lanka to victory against Pakistan, in Galle. He has more or less been a fixture at the Test level since.
"He's such a phlegmatic, calm, relaxed guy - there's nothing excitable about him. He's Mr Dependable. Even with the bat he's got Sri Lanka out of trouble plenty of times. You look at him and you say he's like a club cricketer, but the bloke's mental strength is unbelievable. As mentally strong as any player I've come across.
"When he got called back in 2009, it wasn't like, 'Oh how unlucky am I? Poor me.' He didn't feel sorry for himself. He did what he wanted to do. He put people under pressure, and he changed the game here against Pakistan on the last morning.
"His weapon is his mental strength, coupled with the fact that he's so accurate. There's no mystery to him. What you see is what you get. But don't underestimate him - he'll be all over you. Even if you think you're playing him nicely, he is relentless with his lines and lengths. In Sri Lanka, he is a master of exploiting his own conditions."
Farbrace recalled with particular relish Herath's outstanding figures of 5 for 3 in what was effectively a quarter-final against New Zealand at the 2014 World T20, a tournament which Sri Lanka would go on to win.
"Rangana gave us the turning point of that T20 World Cup," said Farbrace. "We batted first and got 119, and we thought we were done for. The chat in the dressing room was about us knowing they would come hard at our spinners, but if they gave us one chance, we'd have to be all over them.
"Rangana, playing his first game in the tournament, just came on and bowled unbelievably well. Every ball he bowled looked like it could get a wicket. He had McCullum stumped. He had Ross Taylor lbw. Rod Tucker was umpiring at that end, and he said he felt every single ball Rangana was in the game.
"The spell literally turned the game upside-down. We ended up winning the game comfortably, and it just set us on our way to end up winning the tournament. That's the sort of thing that Rangana is capable of. He can turn a game. He looks innocuous, and the people who treat him as innocuous have done so at their own peril. In the subcontinent he's a genius."