The classy left-hander hammered a superb 135 from 202 balls, hitting 15 fours, as Northants piled on 441 for nine in reply to Sussex's first innings of 106 all out.
It was all the more impressive when you consider he arrived at the crease with the County struggling on 60 for four.
Zaib made his Northants first team debut as a 15-year-old, but it has been a long and steady road to him becoming a regular in the senior squad.
Still only 22, the High Wycombe-born player has shown glimpses of what he is all about and the quality he possesses, and last month he hammered a big century for the second team against Derbyshire.
That knock secured the left-hander a spot in the middle order, and although he struggled in the first game at Lancashire, he scored crucial runs against Glamorgan and Yorkshire, before hitting the jackpot against Sussex.
“It is amazing," said Zaib. "It is nice to get it ticked off the list as I have been here quite a long time so it was nice to get it out the way.
“I’ve had plenty of confidence going into today and over the last few games so it was a nice feeling to get over the line."
Zaib shared a 198-run partnership with skipper Adam Rossington, who made 87, and he admitted he feels at home when batting with the captain.
“Adam is very talented and I love batting with him," he said.
"I’ve batted with him on a few occasions over the last few years and he is a very quick scorer so it makes batting a lot easier."
Northants will go into day three in a very strong position, with Sussex still 181 runs in arrears, with only six wickets in hand.
Ben Sanderson and Gareth Berg have taken all 14 Sussex wickets to fall in the match so far, and Zaib said: “Sando’s been doing this for however many years opening the bowling for us and Gareth is really experienced in all conditions so it is nice to have them head our bowling attack.
“They’ve still got a few decent players in at the moment and to come but hopefully we can make a dent in the morning and roll them over as quick as we can."
The one major concern for Northants is the weather forecast, with rain expected for most of Saturday, and things not looking too great for Sunday either.
“I feel like we’re still in a really position in the match," said Zaib. "And even if there is a bit of weather about tomorrow, there is still another day and we back ourselves to bowl them out.”