When the New Zealander took over as head coach in May, Pope was fretting over his place in the squad having failed to fulfil his promise over the course of 23 hit-and-miss appearances.
But rather than cut the 24-year-old loose, McCullum and captain Ben Stokes made a point of inking him into their team and giving him added responsibility with a promotion to number three.
Pope responded by cracking a career-best 145 against New Zealand in his second outing up the order and also managed a pair of fluent half-centuries against South Africa. In seven games since the switch, he averages 38 - well up from a previous mark of 28.66 - and looks a more buoyant figure at the crease.
Reflecting on the shift in tone, he credits McCullum for liberating him.
"I think it's by far the most fun I've had in an England shirt, this summer," he said.
"I had some good chats with Baz, actually, and he's been very much saying, 'stop fearing getting out in Test cricket'. I think it's because Test cricket is so important to me… I'd do anything to have a great career and play 100 Tests or whatever.
"I was almost putting myself under too much pressure and that fear of getting out was probably getting a bit too much. From a guy like him - he's got an amazing record, had an amazing career - he's obviously lived that and lived by that and he realises that along the way, you're going to get a few low scores as well.
"And it's probably about bouncing back from that, looking at why you've got the low score and not overthinking the whole situation."
Pope's newly optimistic outlook was in evidence on the final morning of the final Test against South Africa when, with six needed to win, he attempted to reverse-ramp Marco Jansen over third man.
It was an extravagant stroke, but one which ended up with a concussion test after the ball ricocheted off his glove and into his helmet.
"My wrist wasn't too happy with me making that decision, but I just thought it was a cool way to finish things," he said.
"I guess it sort of sums up a little bit what we're about at the minute. It's just about having fun, entertaining the crowd and hopefully a few wins along the way."
As well as good vibes, Pope also sought some technical advice, hitting the nets with batting coach Marcus Trescothick.
"I realised I needed to change my game slightly and tighten up a few little things which would allow me to become a top-order batter, even though that wasn't necessarily on the radar at the time," he said.
"I did a lot of work with Tres in the West Indies (in March) and before the West Indies as well. I spend a lot of time with him."