The company, which has offices in Leeds, Sheffield, Bishop Auckland and Reading, said the contract from the Just Wills Group creates initial annual recurring fees of £75,000 for the tax and trust department.
The 240 trusts are mainly family trust arrangements but also include disabled trusts and property trusts.
Pearson Jones, which also deals with pensions and employee benefits, said that the contract would also lead to future distribution fees estimated at £300,000.
Jonathan Lee, Pearson Jones tax and trust departmental manager, said: “This significant contract means that we have increased the number of trusts we look after by around 20 per cent and follows the 120 trusts which came into the department last year.
“There is generally far greater tax and trust activity as people wish to protect their wealth more carefully following the recession and ensure that assets do not get taxed where it can be legitimately avoided.
Just Wills, which was founded in 1989, incorporates Willcraft, Willmaster, Legal Services UK, Allguard Legal Services, and In Home Legal Services and has more than 100 national consultants.