The firm secured first place after advising on more than £1 billion of transactions in the region in the last 12 months.
The annual Insider Awards recognise major achievements in the North West corporate, private equity and legal sector.
Corporate partner at Pinsent Masons, Gregg Davison, said:
"We are delighted that the firm's reputation for advising businesses across the energy, infrastructure, financial services and advanced manufacturing and technology sectors has been recognised.
"Pinsent Masons prides itself on its domestic and international profile and we look forward to maintaining such a strong presence and quality of work in the North West region."
The news comes after Pinsent Masons was named the Most Innovative Law Firm in Europe by the Financial Times and achieved more Tier 1 rankings in the latest edition of Legal 500 UK than any other firm.