A writer who penned a piece titled 'How To Murder Your Husband' has been convicted of killing her spouse in the United States.

The jury in Portland, Oregon, took just eight hours to return a guilty verdict against Nancy Crampton Brophy for shooting dead 63-year-old Daniel Brophy.

Prosecutors said the writer, whose 'Wrong Never Felt So Right' series of novels include 'The Wrong Husband' and 'The Wrong Lover', had been struggling financially before she shot her husband twice through the heart in June 2018 at a culinary institute where he worked as a teacher.

The 71-year-old had denied the charge and insisted security camera footage that put her at the scene of the crime showed her scouting for inspiration for her upcoming novel, although she said she had "no memory" of being there.

She also claimed a missing gun which police believe was the murder weapon had been bought as part of research for the novel, and denied that multiple life assurance policies worth $1.4 million that she stood to gain in the event of her husband's demise were a motive for murder.

Investigators said the barrel from the handgun used in the killing was purchased on eBay, and although Crampton Brophy admitted to buying a pistol, she said it was for her husband to protect himself when he went mushroom hunting in the woods.

She added that the missing barrel from the gun was purchased as part of research for an unfinished novel.

Crampton Brophy's lawyers said they would appeal the second-degree murder conviction, The Oregonian newspaper reported.

"Nancy Brophy loved her husband," attorney Kristen Winemiller told the jury at the trial.

"You can see that in her eyes every time she talked about him. Her eyes lit up, they absolutely twinkled," she added.

Crampton Brophy was arrested in September 2018 and has been in custody since, with the murder trial having begun in April.

Prosecutor Shawn Overstreet laid out evidence showing how Crampton Brophy had plotted to kill her husband.

"It's not just about the money. It's about the lifestyle Nancy desired that Dan could not give her," he said during the trial.

Crampton Brophy had rejected claims when she took to the stand last week, insisting that she would be better off financially with her husband alive rather than dead.

"Where is the motivation I would ask you? An editor would laugh and say, 'I think you need to work harder on this story, you have a big hole in it," she said.

The blog post 'How to kill your husband', which is available online, discusses methods and motivations for dispatching an unwanted spouse.

These include financial gain and the use of a firearm, although it notes guns are "loud, messy, require some skill".

"But the thing I know about murder is that every one of us have it in him/her when pushed far enough," the essay says.

Crampton Brophy, who faces life in prison, will be sentenced later.