Former rugby league international Sinfield, assistant coach at Leicester Tigers under Borthwick, joined the RFU ahead of the 2023 Six Nations as defence coach.
After a backroom reshuffle, he was moved to a broader role of skills and kicking coach and will now add a mentoring role with the players, with whom he is extremely popular.
Amid a welter of personnel changes that included new personnel in England's defence and fitness roles, there was speculation that Sinfield would leave but he is to continue, albeit with reduced involvement outside of test windows to allow him to balance other personal and professional commitments.
"Kevin is a talented coach and an inspirational figure in our set-up," Borthwick said. "The work he does on and off the field is invaluable to our players so I am pleased he’ll remain part of the management team."
Sinfield added: "Working with Steve and the team has been an immensely rewarding experience, and I am excited to continue my involvement.
"This new arrangement allows me to keep doing the thing that I’m passionate about, coaching and mentoring players, while also balancing other commitments which are important to me."
Sinfield has raised over £10 million for Motor Neurone Disease (MND) research and charities, sparked by his friend and former Leeds rugby league teammate Rob Burrow being diagnosed with MND in 2019, and has included running seven marathons in seven days as well as other endurance feats.
Burrow died in June but Sinfield’s efforts continue and later this year he will run 50km every day for a week.
Before that he will help England prepare for Twickenham tests against New Zealand, Australia, South Africa and Japan.
