Tom (Matthew Macfadyen) had been aligning himself with powerful people, sometimes at the expense of his relationship with Shiv Roy (Sarah Snook), going back to his betrayal of her in the season three finale, when he gave Logan a heads-up about the siblings' attempt at a coup, therefore proving his loyalty.
After Logan's death, Tom's future as chairman of broadcast news at ATN felt like it was in jeopardy without his father-in-law looking out for him. Being on the chopping block resulted in Tom being constantly stressed and sleep deprived.
In the finale, Tom continued trying to get in Matsson's good graces — and it worked. Over dinner, Tom pitched himself to Matsson by highlighting his managerial skills, his simple approach to the business, his hustle, and his "high tolerance for pain and physical discomfort."
All season, Shiv had been vying for the CEO position. Matsson was in agreement that an American needed to be the CEO, but his confidence in Shiv had wavered for a multitude of reasons, including her lack of experience and pushiness on business decisions. Plus, the boundary between their professional and personal relationship was becoming too blurry, with Matsson even admitting to Tom that he wanted to have sex with Shiv.
Tom, who's compliant and a people-pleaser, quickly moved to the forefront as a contender for the position.
"I'm not looking for a partner," Matsson told Tom. "I'm looking for a frontman."
After Tom assured Lukas that he could be his "pain sponge," he secured his position as the new CEO.