He also faces the possibility of receiving a maximum sentence of 64 to 128 years, Assistant District Attorney Branwen McNabb said.
Dukulah did not testify during his four-day trial in Common Pleas Court. But his daughter and accuser, now 17, testified over two days, telling the jury in graphic detail how her father had sexually assaulted her in every imaginable way from age 8 to 16.
"She showed tremendous strength and courage standing up for herself against the most heinous act that anyone can commit against a child," McNabb said after leaving court.
The girl endured years of assaults without telling authorities, McNabb said, because her mother would not help her and her father threatened that if she told anyone, he would send her back to the family's native country, Liberia, in West Africa.
Dukulah, who had no prior criminal record and was portrayed in court by character witnesses as a churchgoing family man who tutored parishioners, is being held without bail.
Defense attorney Michael T. van der Veen argued that Dukulah was not guilty and that his daughter had told a series of lies about him.
"We're disappointed in the verdict. I believe my client was truly innocent," said van der Veen, who added he plans to appeal.
Dukulah, who immigrated to the U.S. from Liberia in 2006, began teaching in the School District of Philadelphia in November 2011. He and his wife have no other children, van der Veen said.
At the time Dukulah was arrested, Capt. John Darby of the Philadelphia Police Special Victims Unit said there was no evidence that his criminal behavior carried over to the school where he worked.
On Twitter: @MensahDean