McGeechan - a midfielder for Scotland and the Lions in the 1970s - is selecting his all-star XV in a series of articles in London's Daily Telegraph.
He named Kirwan on the right wing and Lomu on the left, with 1970s Wales and Lions great JPR Williams as fullback in the first instalment, published on Monday (Tuesday NZ time).
McGeechan said Lomu was "unique'' and his impact on the sport was "immense''.
"He was built like a train, and could run like one. But he could also really play rugby. Lomu’s skills were honed on the sevens circuit with New Zealand.
"I remember watching him at the Hong Kong Sevens and being absolutely blown away, not only by his size and pace but his footballing ability.''
McGeechan said while illness and injury "ultimately slowed him down'', Lomu's "performances at the 1995 World Cup, just as the game was turning professional, will never be forgotten''.
"The game needed a superstar, and it got one in Lomu. He was brilliant for rugby.''
Kirwan, according to McGeechan, was also "a prototype for what came after him''.
"He was big and strong as well as being incredibly fast. He was a lethal finisher, too. That 80m try against Italy in the first World Cup in 1987 has gone down in history.
"But he had an all round game; he could carry the ball through heavy traffic, he could offload, he was like an extra back-rower at times. Plus, he had natural effortless pace.''
McGeechan said Kirwan, who scored 35 tries for the All Blacks and starred in their unbeaten run between 1987 and 1990, "paved the way for players like Jonah Lomu who would have been making his way through school and the 7s circuit when Kirwan was in his pomp''.