Brady and Theresa met at an AA meeting. Initially the two had a strong disliking for one another. They immediately butted heads, but soon their relationship turned flirtatious. Theresa could tell that Brady wasn't serious about AA, so the two would meet to drink together. Theresa was drawn to Brady and jealous of his rich lifestyle.
Theresa is caught using Abigail Deveraux's ID to buy gifts from a drug store, by JJ Deveraux. JJ blackmails Theresa with the tape in response to Theresa blackmailing him. Theresa blamed Brady for her lapse in judgement. She'd been so enamored with his wealth that she'd let her own guard down. However, this does not stop Theresa from pursuing a romantic relationship with Brady. Theresa turned her attention to her relationship with Brady and she liked how the relationship bothered Maggie Kiriakis, Daniel Jonas and Jennifer Horton.
Theresa's feelings for Brady grew genuine and she turned down advances from another man in favor of focusing on wooing Brady. Brady used Theresa as a distraction as well. Daniel is slipped drugs before he goes into surgery and he and Jennifer both suspect Theresa. However, the true culprit was Liam Frazer. Theresa tried to do damage control, begging Brady to believe that she had nothing to do with what happened to Daniel. Brady said that he wanted to believe her, but if he found out otherwise, she'd be sorry. Brady agreed to help Jennifer find out what happened to Daniel. To do so, he told Theresa that he had to stop drinking and end their relationship and Theresa was crushed.
When the truth came out that Liam was responsible for everything that happened to Daniel and Jennifer, Brady and Theresa resumed their relationship. All of Brady's family disproved of his relationship with Theresa. Despite this, Brady spent more time with Theresa, engaging in heavy partying that included cocaine and the relationship turned sexual. Eventually, he told Theresa that he wanted more from their relationship. Theresa was thrilled because this meant her plan to get his money would be easier.
Brady and Theresa took a trip to Las Vegas. Brady drank heavily and Theresa had to carry him out of the casino. Brady was so drunk that he did not recall Theresa taking them to get married that night. As a passed-out Brady and Theresa flew home on the Titan jet, Theresa looked down at the new wedding rings on their hands. Theresa was thrilled that she had finally landed Brady for good.
Brady's father, John Black was furious when he learned of the marriage. John knew that Brady would get the marriage annulled once he sobered up and yelled at Theresa for being a disappointment to her family. Theresa told John that she would walk away from Brady for $1 million. However, John had been recording their whole conversation and got Theresa's attempted blackmail on tape. Theresa knew that John's tape would mean that Brady would get the annulment. So, she grabbed a fire poker from the fire place and struck John over the head.
John was knocked out cold and Theresa panicked. She dragged John's body over to a passed-out Brady, wiped her prints off the fire poker, and put the poker in Brady's hands. She then screamed for Henderson who called 911. Theresa lied and told the police that John was attacking Brady and Brady swung back in self defense. When Brady awoke in a hospital room, she told Brady the same story and he was horrified that he had hurt his father.
The hit over the head caused John to fall into a coma. Brady started going back to AA meetings and told Theresa that they needed to annul their marriage. He said that he needed to get his life back together. Brady tried to fly in doctors to look at John's case, but they all said that it was hopeless. When Kristen DiMera, Brady's ex-lover, returned to town, Brady returned to Theresa for comfort and to forget about Kristen. Theresa on the other hand, thought there was hope for a reunion between them. Kristen learns Theresa's secret and begins using this information to blackmail her. Kristen also brings to town a doctor with a new formula that would save John. The formula is successful and John wakes from his coma, leaving Theresa to worry that her secret would soon be exposed.
Theresa tries to cover her tracks, but Kristen discovers her secret and gets Theresa's confession on tape. John also begins to remember what happened that night. Everything blows up when Theresa goes to visit John in the hospital. They argue and John threatens to tell Brady that Theresa was the one who hit him with the fire poker, causing the coma. John didn't have to take his threat any further because Brady was right outside the door and overheard everything. Kristen had also gotten a hold of Brady earlier and played the recording for him showing Theresa's guilt. Brady blows up at John and Theresa and doesn't want anything more to do with either of them. Theresa is devastated and argues with John and Marlena. She vows to make things right with Brady. Later, Theresa shares with Anne Milbauer that she believes Brady will take her back eventually because she is pregnant with Brady's child.
Kristen overheard Theresa sharing her news and flew into a jealous rage. She hires two goons to knock Theresa unconscious while she is walking home in the park. The goons take Theresa to a warehouse outfitted with gurneys and other medical supplies. When Theresa awakens in the warehouse, she is dressed in a hospital gown and a doctor approaches her with a needle. Before the doctor pokes her with the needle, Theresa expresses concern because she's pregnant and the doctor confirms that he is well aware of her pregnancy and sticks her anyways, rendering her unconscious again.
Later, Kristen arrives at the warehouse and is wheeled into the room on a gurney also wearing a hospital gown. The doctor asks Kristen if she is ready for the procedure, to which Kristen readily agrees. Kristen vows to get what is rightfully hers. The procedure begins and Brady and Theresa's embryo is transferred into Kristen's womb to be carried by Kristen, as she always wanted to have Brady's child. After the procedure, Kristen leaves town and evidence of Theresa's pregnancy is erased. Brady does not even believe Theresa when she eventually gets the chance to tell him she was pregnant.