During her Auckland years, Jocelyn was Speech Therapist to the North Shore schools and the Wilson Home for Crippled Children from 1952 – 4. An active member of the Mt Eden Methodist Church she participated in the Student Christian Movement, ultimately being appointed treasurer of its Auckland District Council. She planned and fronted the Methodist Church's participation in the Sunday Evening Children's programmes on national radio station 1YA.
In the context of Methodism Jocelyn met and married Fred Marshall in 1954 and they lived in Paris for three and a half years. There they were involved in the life of the British Methodist Church, which was a gathering place for many New Zealand students. They returned to Paris several times on sabbatical leave and, the Methodist Church having been demolished, they worshipped in local Roman Catholic churches. Fred was appointed Visiting Fellow at Corpus Christi, Cambridge and the experience of living in a College and experiencing the long-established routines of college life had a profound influence on her. This broad experience of the hymns and liturgies of the church has been complemented by thirty years spent in the Waikato Cathedral Church of St Peter in Hamilton of which she is now Canon Emeritus.
Jocelyn has been writing poetry for many years. Her introduction to hymn writing came at St Peter's Cathedral. The then dean, the Very Revd Keith Lightfoot, after reading some of her poetry suggested she write a hymn for the patronal festival and it has been sung each subsequent year on that date. This creative strand has flourished until now there are over 100 hymns in the latest collection, Hymns For All Seasons, 2007, which gathers together most of the first collection, A Singing Faith, 1996, with Additional Hymns, 1999 and More Hymns, 2001. Her hymns have also featured in other collections: Sing Glory, Kevin Mayhew, 1999, Carol our Christmas, NZ Hymn Book Trust, 1996, Hope Is Our Song, NZHBT, 2009, Christ's College, Canterbury, Gresham Books, Oxford, 2009 and also on a CD featuring the Waikato Cathedral Choir and the boys choir of Southwell School, Hamilton.
Her hymns trace out the patterns of the Church’s life: baptism, communion, confirmation, ordination, women’s ordination, an installation, synod. They follow the seasons of the Church’s year from Stir-up Sunday through Advent and Christmas to Harvest, Ash Wednesday and Easter; they arise not primarily from liturgical texts although bible passages are there in the background, but are the product of a practical faith built on a positive theology anchored in this world with its joys and sorrows. Sermons recalled are a major source and St Peter's is fortunate to have clergy whose sermons have challenged and inspired. Some hymns are the product of special occasions; many are commissioned by parishes to celebrate their patron saint, and as New Zealand churches pass 100 year and 150 year milestones they look for celebration hymns tailored to their history – the 150th of Nelson Cathedral, the Howick centenary; some mark a significant event – the death of the Princess Diana, or the visit of the Archbishop of Canterbury. At the turn of the millennium God of Ages was written for the hymn competition offered by St Paul's Cathedral, London and was among the finalists from 444 entries in the words section worldwide; one of her carols set by son Christopher won the Auckland RSCM Carol competition in 1993.
Hymns for All Seasons, like the editions which preceded it, draws on the rich treasury of hymn tunes the past has left us, which congregations know and love; and most hymns have a recommended musical setting, carefully chosen to correspond with the mood of the words and appropriate to the metrical patterns. Where the words of old hymns have dropped out of favour, the tunes have thus been resurrected. Hymns Ancient and Modern Revised serves as a convenient and readily available reference for all but a few of the tunes recommended. However there are several hymns where the metre does not fit the patterns available in A&MR. Over the years friends who are composers have set most of these and they are available on the website. Chief among these composers is her eldest son, Christopher Marshall, Paris born, but now resident in America where he is composer in residence and adjunct professor of composition at the University of Central Florida. He has set two of her hymns, three carols and composed several anthems to her words.
Apart from her hymn and poetry writing, Jocelyn has been actively involved in the life of Hamilton. She was associate editor of the Waikato Anglican newspaper Church Alive for fifteen years. For six years, from 1998 – 2004, she was a Hamilton City Councillor; for her involvement with the Save the Children Fund she was awarded life membership of the Waikato Branch. In 1999 she was made a Justice of the Peace and in March 2007 she was honoured with membership of the New Zealand Order of Merit (MNZM).
The words of her hymns are all listed with CCLI (through LicenSing) which make provision for their use in accordance with the guidelines posted on their web site.