Big four firms in Pakistan are;
  • Deloitte
  • A.F. Ferguson (Globally recognized as PwC)
  • EY (Ernst and Young)
  • KPMG
These are not recognized only in Pakistan as the Big Four, But also ranked as the best four accounting firms worldwide. Let's have a look at wikipedia report:
What are Big 4 Firms in Pakistan? Which are Big four Firms in Pakistan? Big Four Accounting Firms, Big four firms in Pakistan
Big Four Accounting Firms

"The Big Four are the four biggest professional services networks in the world, consisting of Deloitte, Ernst & Young (EY), KPMG, and PricewaterhouseCoopers (PwC). They offer audit, assurance services, taxation, management consulting, advisory, actuarial, corporate finance and legal services. A significant majority of audits for public companies as well as many private companies are conducted by the big four.
In the UK in 2011, it was reported that the Big Four audit 99% of the companies in the FTSE 100, and 96% of the companies in the FTSE 250 Index, an index of the leading mid-cap listing companies. Such industry concentration has caused concern and calls for the Competition and Markets Authority (CMA) to consider breaking up the Big Four. In October 2018, the CMA announced it had launched a detailed study of the Big Four's dominance of the audit sector."
If we look at the revenue and employees, Deloitte is the biggest professional services Providing network.
Firm Revenues Employees Revenue
per employee		 Fiscal year Headquarters
Deloitte $46.2 bn 312,028 $148,077 2019 United Kingdom
PwC $42.45 bn 276,005 $153,794 2019 United Kingdom
EY $36.4 bn 284,000 $128,169 2019 United Kingdom
KPMG $28.96 bn 207,050 $139,870 2018 Netherlands