Jason Gillespie will remain as Sussex head coach at least until the end of the 2022 season, after agreeing a contract extension.
Gillespie, who won the County Championship with Yorkshire in consecutive seasons in 2014 and 2015, moved to Hove at the start of the 2018 season but has so far been unable to oversee the side's return to Division One.
However, Sussex have enjoyed more success in one-day cricket, reaching the knockout stages of the Vitality Blast in both of his seasons in charge, including to the final in 2018.
His stature as a coach, including his links to the BBL franchise Adelaide Strikers, has also been helpful in attracting a high calibre of overseas players, including Alex Carey, Mir Hamza, Travis Head, Rashid Khan and Ishant Sharma.
"I'm absolutely delighted to extend my time at Sussex," said Gillespie. "I absolutely love the place and everyone at the club has been fantastic since I joined.
"I really feel we're moving in the right direction, which is really pleasing. I can't fault the efforts of all our players and coaches. We're all on the same page; everyone wants what's best for the club, and I feel we're progressing in reaching those aims.
"We've had some really good times together, and we've had some challenging times, but we're all clear about what we're setting out to achieve and focussed on improving and developing to keep us moving forward.
"That's a pretty special thing to be part of. I want to thank the club for the opportunity to carry on being part of that and for showing faith in me. I'm determined to repay that faith by keeping things moving in the right direction and hopefully having some success down the track."
Rob Andrew, Sussex Cricket's chief executive added: "We are delighted to announce that Dizzy [Gillespie] has extended his contract through to 2022. There is going to be a lot of change in cricket over the next couple of years and we wanted some continuity through this period.
"We still have a lot of work to do to improve the men's side and we were disappointed not to achieve promotion to division one of the County Championship this season. It is where the club aspires to be.
"We have been more consistent in our performances in T20 and 50-over cricket in the last couple of years but need to find that consistency in Championship cricket as well. Dizzy and his coaching team will be working hard to move the club forward and we are delighted he has chosen to help us on this journey."
Meanwhile, Reece Topley has left Sussex after turning down a "long-term contract offer" and deciding "that his future lies elsewhere", the club said in a statement on their website.
Topley, who played 10 ODIs and six T20Is for England between 2015 and 2016, joined Sussex after leaving Hampshire in 2018 following back surgery.
"As a free agent and following back surgery, the 25-year-old was helped back to fitness by Sussex's medical and coaching staff earlier this year before joining the county for the remainder of the 2019 season in July," the statement said.
"Sussex Cricket is disappointed not to have been able to convince Reece to re-sign for the club. Nevertheless, we would like to thank him for his contributions to the team during the season and to wish him well at his new club."