Born on the West Coast, McLennan was a miner and represented the West Coast. He played for the Runanga club. He was first selected for New Zealand in 1951. McLennan played in 84 games for the Kiwis, including 28 tests. This included 22 consecutive tests. His total 84 games has been bettered only by Jock Butterfield (99) and Tom Baxter (94).
He was part of the famous Kiwi team that won back-to-back test series against Australia in 1952 (in Australia) and 1953 (in New Zealand).