The 63-year-old, who is a solicitor by profession, was appointed chief executive of Peterborough City Council in 2002 and took over the same role in Cambridgeshire in 2015.
She had planned to retire last October only to delay this due to the coronavirus pandemic.
After her impending retirement was announced, leaders of the political groups on the city council spoke warmly of Mrs Beasley.
Conservative leader Cllr Wayne Fitzgerald said: “Gillian will be a great loss to the council and the people of Peterborough as she now looks to retire. She has been a great public servant and has truly loved her time here and a she has done a remarkable job for the city.
“I for one will be very sad to see her go, but at the same time I hope she gets to spend more time with her family and friends and can take time out and relax a bit more as she certainly deserves it!”
Green group leader Cllr Julie Howell said: “Gillian Beasley has provided outstanding leadership in Peterborough (and more recently Cambridgeshire) over many years. While her retirement is due and thoroughly deserved we are very sorry to lose her.
“On a personal level, Gillian has given me confidence as the sole female group leader on the council at the moment. I, and the Green group, have benefitted greatly from her professional yet personable approach to every matter that I have brought to her.
“On many levels I will miss her but am glad she will now be able to spend more time on other pursuits having given so much for so long to the city that she loves. Hers will be big shoes to fill.”
Labour group leader Cllr Shaz Nawaz said: “Gillian has been a great ambassador for the city. She has always gone above and beyond and that is a testament to her commitment.
“Gillian has always supported me and I’ve learned a lot from her. She’s a brilliant leader and I will miss her. It was be a loss for the city.
“On behalf of the Labour group I want to thank Gillian for her incredible service. We all wish her all the best for what is a very well earned retirement.”
Werrington First leader Cllr Steve Lane said: “It is always sad to see someone go, but even more so when it is someone that has been a constant in my time as a councillor.
“I have nothing but admiration for the leadership she maintained throughout her time in post. Not only for her style and the way that she worked, but in particular for the dedication to public duty over the past 15 months when she went above and beyond what could be expected of anyone.
“Peterborough will miss her steady hand, but we wish her all the very best for the future and a well-deserved rest.”
Cambridge City Council leader Cllr Lewis Herbert also paid tribute to Mrs Beasley on Twitter.
He tweeted: “Been a privilege & joy to work with Gillian Beasley from when she first joined @CambsCC, shortly after I started. One of the finest UK Chief Executives. Matchless leadership & partnership building, demonstrated again in her steering Cambridgeshire & Peterborough through COVID.”