A US romance novelist who wrote an essay entitled "How To Murder Your Husband" has been convicted of killing her spouse. 

A jury in Portland, Oregon, took just eight hours on Wednesday to return a guilty verdict against Nancy Crampton Brophy for shooting dead 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.

Crampton Brophy, 71, had denied the charge, insisting security camera footage that put her at the scene of the crime merely showed her scouting for writerly inspiration.

She also claimed a missing gun police believe was the murder weapon had been bought as part of research for a novel, and denied the hundreds of thousands of dollars in life assurance she stood to gain were a motive for murder.

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."

Crampton Brophy was arrested in September 2018, and has been in custody ever since.

Prosecutor Shawn Overstreet laid out reams of evidence showing how Crampton Brophy had plotted to kill her husband, who was 63.

"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 of penury when she took to the stand last week, insisting her monetary woes had long been resolved.

"I do better with Dan alive financially than I do with Dan dead," she said.

"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.’"

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

The blog post "How to kill your husband," which is still readily 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.