Calling themselves Justice for Wales, they claimed more devolution supported the case for separation from England.
Former High Court Judge Sir Roderick Evans said legal policies "made in London" were applied to Wales "whether they are suitable for Wales or not".
The Welsh government said a separate system would "simplify devolution".
Wales has shared a legal system with England for nearly 500 years, since the "acts of union" under Henry VIII.
The group, which includes supporters of all the main political parties, said Wales was the only UK nation "lacking its own justice system".
"The economic case for a Welsh jurisdiction is strong and the constitutional case is overwhelming", the lawyers said in a pamphlet launched at the Senedd on Wednesday.
The group claimed a Welsh legal system would encourage skilled lawyers to stay in Wales, and would "bring the courts closer to the people of Wales".
Sir Roderick, now pro-chancellor of Swansea University, said the differences between Wales and England "will increase and become more fundamental as the process of devolution continues".
A Welsh government spokesperson said: "We believe a separate Welsh jurisdiction will develop naturally as the National Assembly passes more Welsh legislation.
"However, there is no doubt that the creation of a separate jurisdiction, as exists in Scotland, Northern Ireland and the Isle of Man, would simplify devolution to everyone's benefit."
In 2012, First Minister Carwyn Jones launched a consultation on the idea, saying: "The development of a legal system fit for a healthy and prosperous Wales is vital."
But the UK government and former Labour Attorney General Lord Morris of Aberavon questioned the need and the cost of such a change.
A separate Welsh legal system could create jobs, cut costs and improve access to justice, a group of lawyers has claimed.