"For over 12 years, Mr Spears has more than capably and dutifully served as the conservator of his daughter's estate, always doing what he believed was in his daughter's best interest," said Vivian Thoreen, Jamie's attorney, in a legal declaration.
"Mr. Spears has performed his job well. This is a fact. He has taken the estate from being in debt and facing tens of millions of dollars of lawsuits, to a current value of well over $60 million.
The new declarations were filed at Los Angeles Superior Court ahead of a Wednesday hearing.
Jamie, nine attorneys representing Britney, her mother Lynne and the conservatorship were live on audio and video connection at the court hearing, due to COVID-19 restrictions.
Judge Penny set new dates in February, March and April 2021 for continued hearings on how the star's conservatorship should be run.
It comes after Britney's lawyer Sam Ingham told the court that Britney was "afraid" of her father and would not perform again until he is no longer in charge of her conservatorship.
Lynne claimed Jamie once told her Britney is "like a racehorse and needed to be handled like one".
Jamie has been overseeing her conservatorship since her public breakdown in 2008. He has not seen her in four months.
This week, he told CNN: "I love my daughter and I miss her very much. When a family member needs special care and protection, families need to step up, as I have done for the last 12-plus years, to safeguard, protect and continue to love Britney unconditionally.
"I have and will continue to provide unwavering love and fierce protection against those with self-serving interests and those who seek to harm her or my family."
