Seven months after he was arrested for defrauding investors of hundreds of millions of dollars and stealing from clients, disgraced attorney Marc S. Dreier was ordered to serve 20 years in prison Monday.

“At this point all I can do is express my shame and remorse,” Mr. Dreier told Southern District Judge Jed S. Rakoff. “I’m sorry to all the people I stole from. I’m sorry to the clients I betrayed. I’m sorry to the lawyers at my law firm for dishonoring their profession.”