Yes, You are eligible for an e-Visa.
Here are the requirements listed on the eVisa website for Pakistani Passport Holders.
You must meet all the requirements listed below in order to obtain an e-Visa. Please confirm that you meet these criteria by clicking the boxes next to them. If you do not meet any of these requirements and you proceed with your application, your e-Visa will be invalid.
- I am travelling for the purposes of tourism or business.
- I can prove that I hold a return ticket, hotel reservation and at least 50 $ per each day of my stay.
- I have a valid Supporting Document (Valid visa OR valid residence permit from one of the Schengen Countries, USA, UK or Ireland). E-visas are not accepted as supporting documents.
- My passport covers the period that I will be staying in Turkey.
- I confirm that I meet each and every one of the conditions listed above.
(The emphasis is mine)
As of today (2018-06-26), the cost of an eVisa for a Pakistani citizen is 60 USD (it varies by nationality). And you can get it within 3 minutes.
What if the supporting visa was single entry and has already been used?
A lot of people wonder about that, You are still eligible even if your supporting visa has already been used, as long as it is valid by date when you enter Turkey.
See this answer: https://travel.stackexchange.com/a/102517/23117