The jury found Stewart guilty on Friday of lying to investigators about her sale of stock in biotech company ImClone Systems Inc.
The eight women and four men returned their verdict on the third day of deliberations, finding Stewart guilty of one count of conspiracy, two counts of making false statements and one count of obstruction of agency proceedings.
In a letter posted on her website immediately after the verdict, Stewart continued to protest her innocence and said she would appeal.
"I will appeal the verdict and continue to fight to clear my name... I remain confident that I will ultimately prevail," she said.
Besides a prison term, the 62-year-old business tycoon also faces a fine of $250,000. Her sentencing has been set for 17 June.
Stewart's stockbroker, Peter Bacanovic, was found guilty on the same counts, but cleared of a separate charge of making false documents.
Stewart showed no emotion when the verdicts were read, but her daughter Alexis broke down in tears.
Although the charges allow for a total 20-year sentence, legal experts have suggested a likely sentence of between one and thee years.
The charges against Stewart stemmed from the trade she made a day before ImClone, the biotechnology company then run by her friend Samuel Waksal, made an announcement that plunged its share prices.
"I will appeal the verdict and continue to fight to clear my name... I remain confident that I will ultimately prevail"
Prosecutors said Stewart received an improper prior-tip that federal regulators would not approve ImClone's anti-cancer drug Erbitux.
Stewart is known as the queen of home decor who amassed a fortune as the head of her own company, Martha Stewart Living Omnimedia.
After the verdict, Omnimedia shares plunged 22.59% to finish at $10.86.