Whilst James’s elder brother William joined their father in the management of the Tooth Brewery, James moved to Tasmania and purchased Ellesmere, a house and estate in the small town of Jericho central Tasmania. He married Katherine (Kate) Augusta Forbes who had also been born in Sydney and was the eldest daughter of Judge Forbes of the District Court of New South Wales.

James and Kate Mitchell lived at Ellesmere for some years. James was involved with both the Royal Hobart Golf Club and the Hobart Yacht Club. His brother William was also a keen sailor and a member of the Sydney Yacht Club.

James and Kate were generous supporters and workers for the Red Cross during the First World War and later made Ellesmere House available as a convalescent home for returned sailors and soldiers.

James died in 1930. He left his estate of £21,566 (£1.3m today) to his widow with made certain private bequests to relatives and friends. He provided £1,000 to the trustees of the Church of England in Tasmania. It stipulated that of the amount £250 shall be for the Jericho Endowment Fund for the stipend of the clergyman in charge of St James's Church, £500 for the benefit of the clergy superannuation fund and £250 for the general church fund. Bequests of £250 each were made to the Alexandra Hospital Hobart, the Salvation Army Hobart, the Blind Deaf and Dumb Institution and the Tasmanian Sanatorium. His house and land at No.1 Greenland Avenue, Sandy Bay he left to his nephew Graeme S. Bisdee. And the trustees were directed to sell the estate at Ellesmere.

A stained-glass window the gift of Mrs J G Mitchell was dedicated at St. David's Cathedral to the memory of James Graham Mitchell by the Dean of Hobart the Very Rev. A. R. Rivers. ‘The window which is the first of a series of six chancel clerestory windows on the Holy Spirit is very rich in its colours and remarkably clear. The theme is St Peter and St John in Samaria at the laying on of hands.’ The work was carried out by Brooks Robinson Ltd of Melbourne. After a short prayer and the reading of a lesson from Isaiah, the Dean paid a tribute to the late Mr Mitchell whom he characterised as having been one of those who look on what they have as a trust for the use not of themselves alone, but others. He said that during his long friendship with Mr Mitchell he had always found him courteous, helpful, good and reliable and one in whom the fine qualities of an English gentleman had shown themselves in small things and in great. Among those present were Mrs J O Mitchell, Mr and Mrs. Graham Bisdee and Miss Bisdee, Mr and Mrs Rex O'Kelly, Mr and Mrs C W Butler, Mr and Mrs Dennis Butler, Sir Elliott and Lady Lewis. Mrs Mary Parker OBE (representing the Red Cross Society) Mrs E H Webster, Messrs. Geoffrey Walch, R. Seager (representing the Royal Hobart Yacht Club), J. R. Crane, P. S. Shadforth and E. H. Pearce, Mr. and Mrs. V. I. Chambers, the Rev. J. A. Cloudsdale and Messrs Hughes; Ryan, Briggs, and Williams.

After her husband's death Kate Mitchell made a gift to St. John's Church of England Hospital to enable a wing to be erected to be dedicated to the memory of her husband and to be called ‘The James Graham Mitchell Memorial Ward.’ One of the conditions was that three beds built in separate cubicles were to be kept for women whose incomes would not permit them to pay fees in a private hospital. A newspaper report at the time stated: ‘Facilities at St. John's Hospital, Hobart, have been extended by the addition of a new wing, which was opened on Saturday by the Governor Sir Ernest Clark and Lady Clark. The opening was attended by the Bishop of Tasmania the Rt Rev Dr R S Hay and Mrs J G Mitchell widow of James Graham Mitchell in whose memory the new wing was built, following the magnificent gift of approximately £11,000 by Mrs J G Mitchell for the erection and endowment of the James Graham Mitchell memorial section of the hospital.

Archdeacon D B Blackwood chairman of the hospital board of management, later reported that the entire cost of the new wing had been borne by Mrs. Mitchell. The board was co-operating to the extent of providing extra kitchen accommodation and provision for extra nursing accommodation.

Kate Mitchell also took a great interest in and was a generous friend to the Clarendon Children's Home. She also was a substantial subscriber to the Church Huts for Soldiers.

Kate Mitchell died in 1947. The newspapers reported: ‘Death Of Mrs K Mitchell, Philanthropist. The death occurred last evening at her residence, King St., Sandy Bay, of Mrs Katharine Augusta Mitchell, widow of Mr J G. Mitchell. A service is to be held in St. David's Cathedral tomorrow at 3 pm. The funeral will take place at Cornelian Bay.'