A rogue and scoundrel at the best of time, Jason obviously learned early that good manners and a charming facade would get him further in his schemes. Little is known of his family or background, and what is known is unreliable, as it came from Jason himself. For instance, his name suggests an Irish background, but his accent slipped often enough to be unsure of that. But we do know that sometime in the 1940's he met Paul Stoddard. The two recognized each other as kindred spirits and became fast friends.
By 1949, Paul had married Elizabeth Collins for her money, and now was ready to get out. Jason helped Paul plan his exit, arranging for ways to turn the bonds and jewelry Paul would take from Collinwood into ready cash. But when he came to pick up Paul and the money, he met Elizabeth in the foyer. He was shocked to find out that she had hit Paul with a poker to keep him from leaving with Carolyn's inheritance. Jason went into the drawing room alone to check on Paul, and found him dazed and bleeding on the floor. Never one to overlook an opportunity, he told Paul to leave the back way and wait for him at the Blue Whale. Then he went to Elizabeth and told her Paul was dead. Going through the entire charade of burying a trunk in the basement, Jason convinced Liz she was guilty of murder. Then he and Paul left Collinsport together, travelling the world and running their schemes. It was about eight years later in Hong Kong that they parted ways (probably running in different directions from the authorities).
Jason continued his schemes in a variety of countries over the next ten years (earning outstanding warrants in most of them) with varied success. At some point he also met a new partner, a coarse young man named Willie Loomis. By 1967, they had run into a streak of bad luck; they were broke. Jason decided it was time to cash in on his nest egg. They would go to Collinsport.
Leaving Willie at a motel outside of town, Jason went to the Blue Whale. He was surprised to learn from Maggie Evans that Elizabeth Collins Stoddard had not left Collinwood for eighteen years. (But it was probably a pleasant surprise, as it confirmed she had not learned the truth.) Showing up at Collinwood, he told Liz he was moving in. She was unable to refuse, as he knew she would be. Jason planned to arrange for Willie to join him once he had prepared the way, but Willie got impatient, showing up and thanking Jason for inviting him to stay.
As Jason had suspected, his control over Liz wasn't strong enough yet to tolerate Willie. His harassment of Carolyn and Vicki was too much. She demanded that Jason make Willie leave. He agreed, but oddly, he was unable to find him. he did track him to the Collins' mausoleum at Eagle Hill Cemetery, but found no further trace of him until he came back to Collinwood sluggish and subdued. Assuming he was ill, Jason tried to convince Liz to let him stay, but that didn't last long. Luckily, Willie soon moved into the Old House as handyman for Barnabas Collins. Jason was extremely suspicious of this since Willie had never done a day's work in his life. Little did Jason know his old partner had fallen under the spell of a vampire.
But he was too busy enjoying life at Collinwood to worry too much about Willie. His control over Elizabeth grew stronger daily. He blackmailed her into making him Vice President of Public Relations of Collins Industries, drawing a healthy salary. But everyone in the house was convinced Jason had something on Liz, and that it was connected to the locked room in the basement. So McGuire came up with his most audacious plan yet. Elizabeth would take the family into the room (after he had checked it out, though he knew there was nothing to find anyway), "prove" he had no hold on her - then announce their engagement. Believing she would lose her daughter if she knew the "truth", Liz followed his orders. Now Jason was sure his hold on her was complete.
Not that anyone had given up. Roger made plans to get Liz to sign papers keeping Jason from getting any money from the marriage. Knowing Liz would never sign, Jason practically laughed in his face. He was just as unconcerned with the implied threats of Barnabas Collins, though he seemed to enjoy the mental sparring. (If he had known a little more about Barnabas, he might have been somewhat more concerned.) He was worried about Carolyn, however, knowing Liz's concern for her daughter was the one thing that could stop him. So when she announced that she would marry motorcycle punk Buzz Hackett if her mother married Jason, he tried to bribe Buzz into leaving Carolyn. That failed, but he needn't have worried. Elizabeth was so terrified the truth would be discovered, she would do anything Jason wanted.
His power over Liz made him extremely confident. When Burke Devlin tried to tell Elizabeth about all of Jason's previous wrong-doings, Jason just laughed and invited him to the wedding. He even told Carolyn he wanted her out of Collinwood immediately out of the wedding. (Actually, this would have been a smart move, as Carolyn's continued presence might have eroded his hold over Liz, if it hadn't prompted Carolyn to get a gun to shoot Jason during the wedding.) But Jason should not have been so sure of himself. For Elizabeth, tormented for years and pulled in so many directions, decided to clear the air and tell the truth as they stood in front of the judge. She announced to the gathering that she had killed Paul Stoddard, and that Jason had helped her cover it up. Jason shielded himself with the truth (for once), saying their was nothing in the basement, but no one believed him. His instincts taking over, Jason fled into the woods around Collinwood. It was only a few hours later that he was caught, and the sheriff had already discovered the trunk in the basement was empty. Elizabeth wanted an explanation, so he told her what had really happened - in exchange for her dropping the blackmail charges.
Jason wanted to get out of town as soon as possible, but he needed money. He certainly wasn't going to get it from Liz. To what he considered his good fortune, he overheard Barnabas' plans for Victoria Winters. Using the information, he made Willie steal from Barnabas, but to his disgust Willie only brought him one piece of jewelry. As it was hardly enough to satisfy the greedy Jason, he ignored Willie's pleas to leave Barnabas alone and broke into the Old House. It was the last mistake Jason would ever make. For the vampire was awakening, and Barnabas killed Jason McGuire, burying him in the secret room of the Collins mausoleum. Everyone assumed he had just skipped town, and Jason laid in his grave unmourned.
