To establish an ineffective assistance of counsel claim the client must, first, prove their lawyer's representation fell below an objective standard of reasonableness. Second, the client must prove the deficient performance resulted in prejudice.
Failure of defense counsel to inform a client of plea offers made by the prosecution is an omission that falls below a standard of professional reasonableness. Furthermore, courts have been unanimous in finding that defense counsel's failure to inform a client of a plea offer constitutes a violation of the person's Sixth Amendment constitutional right to effective assistance of counsel.
But the failure to advise the client of the offer is not quite enough to obtain a reversal. The client must also show they were harmed by the lawyer's unprofessional conduct. In other words, the client must further prove they would have accepted the plea offer had it been communicated. Luckily, the courts have not required defendants prove the trial court would have accepted the plea bargain to establish harm. Only that the defendant missed the opportunity of accepting such a bargain and presenting it to the trial court for consideration.
If you find out your lawyer failed to communicate a plea offer to you, contact new defense counsel immediately. Relief might be available and you need to discuss the matter with an informed and experienced criminal defense lawyer as soon as possible.