Slack made his Middlesex debut in 1977, but failed to establish himself in the side, in part because he played out of position, in the
middle order. When
Mike Brearley, Middlesex captain and batsman, was recalled to the
England side in 1981, Slack was called on to replace Brearley and open the batting for Middlesex against
Kent at
Lord's; he scored his maiden first-class century, 181
not out. This auspicious opening with Barlow foreshadowed their profitable partnership, one of the best opening pairs in the County Championship circuit of that era, 85 in the third unofficial 'Test', and 122 not out in the last unofficial 'one day international'.
Simon Hughes wrote of him in
A Lot of Hard Yakka: "Wilf Slack, a reserved Windward Islander who never betrayed any nerves despite the daily task of standing up to some of the fastest bowlers in the world, rarely said anything when he came back into the dressing-room. He’d sit down, quietly unbuckle his pads, and carefully lay them to rest in his case, then stare glumly into space for a while. He was deeply religious, which was possibly an explanation for such contemplation". Besides holding nearly 200 catches, many at bat-pad, he was always eager to bowl his military-medium pace, especially in limited-overs matches. ==International career==