Smith, 58, pleaded guilty to second-degree murder last month.
She gave Lewis and his new girlfriend, Thanyarat Nina, insecticide-laced Jagermeister. Lewis died while Nina survived.
Smith also pleaded guilty to second-degree assault for the poisoning Nina.
Judge Tim Bradshaw agreed with senior deputy prosecutor Carla Carlstrom who recommended 20 years in prison for Smith.
Bradshaw called the crime "cold-blooded," not a crime of passion or self-defense as was portrayed by Smith's attorney.
Smith asked the judge for mercy.
"I am asking the judge to please be compassionate and asking for your honor's kindness," Smith said.
He showed little and Smith received the high end of the standard range for this crime. She will get credit for the 1068 days she has already spent in custody, from Dec. 4 2008, until now.
According to court documents, Smith and Lewis had been in a relationship for 18 months, and the two had even lived together in Kirkland for a time.
In September 2006, Lewis returned from a trip to the Philippines and broke the news to Smith: He had met someone else whom he planned to marry.
"Smith reportedly did not receive this news well," a detective wrote in court documents.
The woman tried to persuade Lewis to stay with her. She left for a trip to Japan, and when she returned in early October, Lewis would have nothing to do with her.
At some point, Smith learned that the new girlfriend, Nina, was going to meet Lewis for dinner. On Oct. 6, 2006, Smith called Nina and advised her that Lewis was fond of Jgermeister and liked to have a drink before going out for the evening.
She offered to send a bottle over and urged the woman to make sure Lewis had a drink before they left for dinner, according to charging documents. Smith enlisted the help of a man she knew to deliver the bottle.
Prosecutors contend Smith had laced the alcohol with the insecticide methomyl.
When Lewis arrived at Nina's apartment about 6:30 p.m., she offered him a drink. Lewis drank a full shot glass, and Nina drank about half a glass.
Almost immediately, Nina felt ill, lost her vision, then blacked out. A friend found the woman blind and disoriented in the apartment. Lewis, 56, was face down on the floor, dead.
Investigators determined days later that the alcohol had been poisoned. By then, Smith had flown to Los Angeles and left the country, using tickets her daughter had bought her to go to Taipei.
Authorities were certain that Smith had gone to Thailand and worked with law enforcement there to track her down. In 2008, Smith flew to Switzerland, then to London, where she was caught.
Smith was originally held on $5 million bail.