The growing Central Square district helped Cardiff top the UK charts for property deals involving law firms in 2016.
Blake Morgan moved into a 28,077 sq ft (2,608 sq m) office, while Hugh James will take up a 100,000 sq ft (9,290 sq m) site when it is completed in 2018.
Knight Frank's research showed 19.2% of property deals in Cardiff in 2016 involved law firms.
BBC Wales will also move into its new headquarters at Central Square in 2019.
And it was announced last week that HM Revenue and Customs will move 4,000 staff from Llanishen to a 266,000 sq ft (24,712 sq m) site there.
When it is fully developed, the former bus station area will include up to one million sq ft (92,903 sq m) of new office, residential and retail space.
Chairman of Central Cardiff Enterprise Zone, Chris Sutton, said the decisions of Hugh James and Blake Morgan to move into top quality accommodation at the site was "reflective of their growth into national UK players".
Knight Frank's Matt Phillips said the rise of Central Square and the presence of such companies could help turn the city into a hub for the legal profession.
He said with London-based firms looking to outsource because of the costs there, Cardiff could become "extremely attractive".