England's withdrawal infuriated the Pakistan Cricket Board, who called it "disrespectful" as they made strides to show the country was a secure destination.
England, the current 50-over world champions, are also scheduled to play a Test series in Pakistan in December followed by the return of New Zealand.
The tourists are looking to bounce back from recent Twenty20 series defeats to the West Indies (3-2), South Africa and India (both 2-1).
Pakistan are looking to recover after losing the T20 Asia Cup final to Sri Lanka in the UAE last week.
New England skipper Jos Buttler, who took over after the retirement of long-time captain Eoin Morgan this year, is nursing a calf injury that could keep him out of the series.
"It's an important series for the build-up towards that World Cup," said Buttler, who felt it was vital to travel with his side despite only having a chance of being fit for the final two matches.
"Obviously the main aim for everyone is to turn up fully ready for that World Cup," said Buttler.
"Pakistan are a very strong team and will give us a really tough challenge," added Buttler.
Moeen Ali will lead the side in his absence.
The return of explosive opener Alex Hales from three years in the wilderness after testing positive for a recreational drug will bolster England batting, according to Pakistan's top order batsman Shan Masood.
"I think England are one of the best white-ball teams," said Masood, who will make his Twenty20I debut for Pakistan as a reward for scoring heavily for Derbyshire in the English T20 Blitz.
"England will pose a very good challenge for us and it's probably the ideal preparation to play one of the best sides before the World Cup."
The first four matches are in Karachi on 20, 22, 23 and 25 September with the final three in Lahore on 28, 30 September and 2 October.
A head-of-state style security cordon is being thrown around the England entourage, similar to that successfully employed for the Australia tour.
Officials said 4,000 police and paramilitary personnel will be on duty to guard the teams and stadium on match days.
Spectators will have to park at least a mile from the venue and be brought to the stadium in special secure shuttles after undergoing thorough bag and body searches.
Squads for seven-match Twenty20 international series in Karachi and Lahore from 28, 30 September to 2 October:
Pakistan: Babar Azam (captain), Shadab Khan, Aamer Jamal, Abrar Ahmed, Asif Ali, Haider Ali, Haris Rauf, Iftikhar Ahmed, Khushdil Shah, Mohammad Haris, Mohammad Hasnain, Mohammad Nawaz, Mohammad Rizwan, Mohammad Wasim, Naseem Shah, Shahnawaz Dahani, Shan Masood and Usman Qadir.
England: Jos Buttler (capt), Moeen Ali, Harry Brook, Jordan Cox, Sam Curran, Ben Duckett, Liam Dawson, Richard Gleeson, Alex Hales, Tom Helm, Will Jacks, Dawid Malan, Adil Rashid, Phil Salt, Olly Stone, Reece Topley, David Willey, Chris Woakes, Luke Wood and Mark Wood.