Det Supt Andy Brennan, who led the investigation, described Matthews as "pure evil".
"It is difficult to understand what type of woman would subject her own daughter to such a wicked and evil crime," he said.
During the three-week trial, the court heard that Shannon, now 10, went missing on 19 February as she walked home from school.
After a huge search operation by West Yorkshire Police costing almost £3.2m, she was found by police in Donovan's flat, less than a mile from her home, on 14 March.
The search was one of the largest ever conducted by the West Yorkshire force.
The prosecution told the jury that Donovan kept Shannon drugged and imprisoned in his flat as part of a plan he and Matthews hatched to claim £50,000 in reward money.
Matthews denied the abduction and blamed the crime on her former partner, Craig Meehan, and other members of his family.
She said she was "disgusted" by allegations that she was involved in her daughter's kidnap.
I'm a mum myself and know I would have been out of my mind and Karen didn't seem to be
Det Con Christine Freeman
Donovan, who is the uncle of Mr Meehan, claims he was scared of Matthews and agreed to take Shannon only because he feared for his life.
Neither of the defendants showed any emotion as the jury foreman returned the verdict.
Matthews stood staring straight forward in the stone-coloured jacket she has worn throughout the proceedings and with her red hair hanging untied over her shoulders.
Donovan, who had been described in court as "a dimwit" stood a few feet away from her, separated by a court security officer.
The court remained silent following the verdict after the judge warned the public gallery against over-emotional responses.
The seven men and five women on the jury took about six hours to find the pair unanimously guilty of all charges.
Police interview Karen Matthews
After they returned their verdict, Mr Justice McCombe thanked the jury for their "careful consideration" throughout the trial.
The judge said: "You have done it with great aplomb and behaved with great dignity."
Malcolm Taylor, from the Crown Prosecution Service, said the actions of Matthews and Donovan amounted to an "abuse of public trust".
"This cynical plot culminated in Matthews's television appeals for the return of her daughter, made while she was actively concealing the whereabouts of the child from the police, who were deploying huge resources to search for Shannon."
Mr Taylor said the people of Dewsbury were duped into giving "unstinting assistance to the hunt for a defenceless child whom they thought was missing during the coldest part of the year".
Family liaison officer Det Con Christine Freeman said she received a telephone call within minutes of meeting Matthews who then started dancing to the ring tone.
"I remember thinking how odd to be dancing to my ring tone when your daughter's missing.
"'I'm a mum myself and know I would have been out of my mind and Karen didn't seem to be," she said.
Det Con Freeman said Matthews looked "foolish" during the trial by continuing to deny her involvement.
"I would just like her to tell the truth," she said.
MICHAEL DONOVAN'S FLAT WHERE SHANNON WAS HELD CAPTIVE
The court was told Shannon was tied to an elasticated strap tied to a beam in the hallway. It would have restricted her movements and prevented her from reaching the front door.
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