Proceeds of the issue, sponsored by James Capel, will go to Towry's existing shareholders. No new money is being raised for the company. It is coming to the market to facilitate acquisitions.
Towry Law was set up almost 35 years ago as a life insurance broker but expanded into general insurance and financial planning.
The group, which employs 400 staff, has more than 60,000 private and 5,000 corporate clients.
It incurred an pounds 89,000 operating loss in 1989 due to poor managerial control. Since then a new team has lifted taxable profits from pounds 1.3m in 1990 to pounds 2.4m last year.
The shares are to be priced on 4 November and dealings are expected to start a week later.