Bloomfield had been out of work since he was sacked as Luton boss in October 2025.
He was appointed by Oxford at a time when they were 23rd in the Championship, three points adrift of safety, coming in after Rowett had overseen a dismal spell of one win in 10 matches.
Bloomfield began his managerial career at Colchester United before taking over from Gareth Ainsworth at Wycombe Wanderers in 2023.
After leading the Chairboys to the League One automatic promotion places amid the challenge of big-spending Birmingham City and Wrexham last season, he left to take over at Luton.
But Bloomfield was unable to prevent the Hatters from suffering back-to-back relegations to the third tier and was dismissed after an underwhelming start to the season, with the club 11th in the table.
Speaking after Oxford's relegation was confirmed in April, Bloomfield said he was confident of keeping his job.
"I've enjoyed my time at the club. It's obviously not been the outcome that we wanted for the season," he said.
"We've been pleasantly content with some of the improvements we have made but ultimately we wanted to stay in the league.
"I've not given much thought to my job and the bigger situation and ultimately, as a manager or head coach, all you can do is focus on being the best you can be."
Oxford looked capable of pulling off a "great escape" in late February and early March when they won three games in a row to move up to 21st.
However, just two wins in the following eight matches saw them lose ground on the sides above them.
Relegation brought an end to a two-year spell in the second tier after they won promotion via the League One play-offs in 2023-24.