Nicola Clemo, who joined Slough Children's Services Trust in July 2015, ahead of its official launch in October 2015, said she plans to retire at the end of April in order to spend time with her family.
The decision comes just days after the publication of the findings of the latest Ofsted visit to monitor progress at the council after provision was rated "inadequate" in February 2014, and again in February 2016, after it had become a trust.
During the monitoring visit, inspectors said a lack of supervision and oversight of social work means that children's services leaders cannot be certain that all children are receiving good support. It was also found to be leading to delays in taking action when children were at risk.
"This continues to be an area of practice that requires attention. This has hampered progress in some areas and consequently, the pace of improvement has been slow."
The letter acknowledges that the council is taking action to improve the way managers supervise social workers, but adds: "Inspectors saw some considerable gaps in supervision taking place.
"Management oversight lacks rigour and managers are not stringent enough in making sure that children's plans are progressed. As a result, there is sometimes drift and delay in taking action when risks to children increase, or progress is limited or not sustained."
Inspectors welcomed efforts by the trust to improve workforce stability, finding that 81 per cent of social workers are now permanent, compared with 72 per cent in January 2017.
But some social workers still face excessive workloads, inspectors said.
"Caseloads have reduced overall and most social workers have manageable caseloads. However, there are some disparities, with a very small minority of social workers holding caseloads in excess of 30 children," the inspectorate's letter states.
Three days following the publication of the findings, Clemo announced she would be retiring.
"This has been an incredibly hard decision for me, but I have made the decision to retire," she said.
"I have been thinking seriously about it for a while and I will be leaving at the end of April. I shall feel very sad to leave such a fantastic workforce but after almost three years at an unbelievable pace, I have decided that I need to slow down and spend more time with my family."
Robert Tapsfield, the chair of the trust's board said: "Nicola's dedication and hard work has put the trust on the path to success. We are all very sorry to see her go but she has worked tirelessly to get the trust to where it is now and all of us are very grateful to her for her passion, commitment and energy.
"The timing of Nicola's decision to retire now is to fit in with family commitments and is not related to the publication of the latest Ofsted monitoring visit. She had hoped to see the Trust through its next full inspection but, as that is now delayed, she had to make a difficult decision. She made that on the basis that the Trust - despite the improvements we are aware we need to make - is in the strongest position it has been for some time. We respect her for that.
"We have a strong leadership team in place and we will look to recruit an interim before Nicola goes. She has been a very dynamic and strong leader and will leave hard shoes to fill, so we will take our time to recruit a permanent replacement."
The pace of progress in Slough is in contrast to that in Doncaster, the first children's services trust to be established on the orders of the DfE, where a re-inspection last month by Ofsted saw standards upgraded from "inadequate" to "good".
The monitoring visit to Slough was one of two carried out in January, with inspectors also visiting Tameside Council.
During Ofsted's visit to Tameside, which was judged "inadequate" in December 2016, inspectors praised improvements since the council appointed a dedicated director of children's services in October last year. This appointment was made after the role was separated from adult services the previous month.
"Since their appointment, the DCS has led work to re-evaluate the current position and accelerate improvement," states Ofsted in a letter to Tameside Council.
"The local authority now has an accurate self-assessment. It demonstrates a good understanding of the scale of change required in systems, culture and practice."
Inspectors also found improvements in management oversight of cases, an increase in the number of social work posts and that referrals for children were progressing swiftly.
However, concerns remain around poor record keeping with case notes missing vital information from health services and police.
"This means that children's and parents' needs are not fully understood," adds Ofsted's letter.
Tameside Council has been contacted for comment.