Hadlee married Lilla Monro in 1940. They had met on the ship to England in 1937. They had five sons. He took great pride that three of his five sons represented New Zealand: Dayle, a Test fast bowler, and Barry, a batsman in the inaugural 1975 Cricket World Cup, were eclipsed by Richard, who became a leading all-rounder: he took 431 Test wickets – a world record at the time – and 1,490 first class wickets, and also finished with a Test batting average of 27.16. Richard was knighted for services to cricket. A fourth son, Martin, played club cricket in Christchurch.