Singapore's oldest law firm is combining forces with law firms from the United States, Australia and China to boost its global reach.

The combination involves Rodyk & Davidson linking with Australia's Gadens and American giant Dentons, which became the world's biggest firm earlier this year when it joined forces with China's largest law firm, Dacheng.

Rodyk will be renamed Dentons Rodyk & Davidson. It will be licensed as a Singapore firm and continue to operate as an independent partnership.

Mr Philip Jeyaretnam, a senior counsel, will be global vice-chair of the combined firm and will also remain the managing partner for the Singapore operations.

It will mean Rodyk's 200 lawyers in Singapore combining with Gadens' 500 lawyers and the 7,000-plus lawyers at Dentons Dacheng. The move will also give Dentons more than 80 offices in the Pacific Rim.

Under the deal, the firms' profits and tax, accounting and partner compensation systems will remain separate while they will combine to share strategy, branding and information technology.

Voting by the partners on the proposed combination is expected to end later this month, with the combined entity starting operations next year.

Its annual revenues are estimated to be between US$2.01 billion (S$2.8 billion) and US$2.14 billion.

The move is driven by the fact that more than half of Dentons' 200 largest clients do business in Singapore and Australia.

Other factors include China's growing investment in infrastructure development in South-east Asia and the South Pacific, as well as potential opportunities afforded by the Trans-Pacific Partnership.

It will also allow Rodyk to grow its client base by enhancing its ability to deliver certain types of work and by connecting lawyers in various countries with its client base.

"We have had inquiries from clients looking for help in Australia and the UK. Previously, we have had to work with unrelated firms to assist them. Now, we can work with Dentons to help them," Mr Jeyaretnam told The Straits Times.

"We have also had inquiries about Africa, which is a new jurisdiction for us," he said.

"It's hard to find a global firm that has a footprint in Africa. But Dentons has a strong network there. Now, we can assist our clients venturing there," he said.

Gadens chairman Ian Clarke sees the move as an opportunity to develop a "more effective solution for its clients going overseas, and for those making inbound investments into Australia".

Singapore, in particular, is a significant market for the firm as it represents the second-largest source of inbound investments to Australia.

Some of Gadens' clients are also relocating their headquarters from Houston and Vancouver to Singapore, so Mr Clarke sees the need to be represented in Asia "far more deeply than ever before."

Mr Jeyaretnam noted that Rodyk's practices that have a global element, such as arbitration, mergers and acquisitions, and competition law, will likely benefit faster.

"If there is a competition investigation in the US, there will likely be parallel probes in Europe and Asia. Because of the global nature of the practice, the firms can coordinate their resources to handle different investigations," he said.