Maddinson has scored 0, one and four in his three test innings since making his debut against South Africa in Adelaide and his place in the team had been in question following the decision to call all-rounder Hilton Cartwright into the squad.
Smith, however, said Maddinson would play at the Melbourne Cricket Ground on Monday as his fast bowling trio of Josh Hazlewood, Mitchell Starc and Jackson Bird had recovered well after a heavy workload in the first test in Brisbane.
The trio bowled 113 overs between them in Pakistan's second innings, where the visitors were dismissed for 450, chasing 490 for victory.
"We brought the all-rounder into the squad because the bowlers had a pretty heavy workload but they've pulled up well and they're confident they can get through," Smith told reporters on Sunday.
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"Obviously (Nic) hasn't started the way he would have liked. I was really proud of him in the second innings in Brisbane to come out and do the thing for the team and try and score quick runs and have a crack.
"That's what we want from our team, to have unselfish players like that and I thought he did a good job to come out and do that."
Despite winning the match in Brisbane, Smith has been criticised for not being ruthless enough when he failed to impose the follow on when Pakistan were skittled for 142 in their first innings, 287 runs short of Australia's total.
His cautious field settings on day five, with Pakistan still needing 108 runs for victory with only two wickets in hand, were queried by former captains Michael Clarke and Mark Taylor and slammed as "ridiculous" by ex-England skipper Michael Vaughan.
"People are open to criticise me all they like but in the end, we won the test match so I'm happy with that," Smith added. "You can always learn from different things."
It was the second successive test victory for the side, which had been overhauled following a humiliating innings and 80-run loss to South Africa in their second test in Hobart, which sealed the series for the Proteas.
The Hobart loss was Australia's fifth in succession and the selectors swung the axe with five changes to the team for the third game in Adelaide.
Smith's revamped side responded with a seven wicket victory and continued that momentum with victory in Brisbane.
"I'm really happy we won the test match," Smith said of the Brisbane game. "That's five wins in a row (including three one-day matches against New Zealand) so we're heading in the right direction."
(Reporting by Greg Stutchbury in Wellington; Editing by Andrew Both)
