Smith was consistently prolific, publishing poetry, fiction, translations and essays throughout his adult life. His first collection of poetry was published in 1955 - a short paperback volume entitled The Long River. This was followed up by a number of collections, including his fifth in 1965, The Law and the Grace. This collection features one of Smith's famous 'Old Woman' poems, a meditation on the negative impact of Free Presbyterianism on the human spirit. This is followed up in 'The Witches' and 'Old Highland Lady Reading Newspaper'. Reflections on Highland culture are often interspersed with references to world figures with universal shared connotations, such as Freud and Dante, and - in this collection - the poem 'Lenin'. Drawing from his own restrictive background did not provide every necessary mode of expression; Smith was required to dip his pen in the wider world also, 'the endlessly various, real, human,/ world' alluded to in the poem. The eponymous poem, 'The Law and the Grace', is expressed with a controlled anger at the restrictions of his work and his context, foregrounding the contradictory nature of the two forces of 'law' and 'grace', both poetic and religious. Contradiction provides the dynamic for much of Smith's work. Through this he seeks a poetic freedom.

Smith was primarily a poet, however his first novel, Consider the Lillies (1968), has achieved some critical appreciation for its moving portrayal of another 'old woman', the widowed and isolated Mrs. Scott (note the symbolic name, the suggestion that she is a synecdoche for the nation). Again, a struggle between law and grace is evident, between Presbyterian repression and physical and spiritual pleasure. The novel is written in English and set in the time of the Highland Clearances, again picking up a prevalent theme in the poetry. Yet it is not a historical novel as such, as Smith asserts in his own preface to the tale, but rather a study of one individual's struggle to cope and adapt against a background of flux and disruption. The style of the narrative is somewhat simple, with sparse understated language used to represent the thoughts and emotions of Mrs. Scott herself, and to allude to the uncomplicated Gaelic that would have been used by such a community. Ultimately, however, the novel articulates a universal admonition that goes beyond Gaelic Scotland; the dangers of unquestioningly accepting any ideology - whether Calvinism, Capitalism or some other system of beliefs - are highlighted, while the essential kindness and community of the human spirit is celebrated.

Smith also wrote short stories, and one of his best tales is the 1973 An t-Adhar Ameireaganach, 'An American Sky', the revealing story of an exile's return to his home island after economic migration to the States. What the protagonist finds on his return, in particular the hybridisation of the 'pure' culture he left behind, disappoints and even disturbs him. Yet through the pertinent narrative perspective, Smith manages to serve a critique on both rapid change and those who would wish to preserve such communities like museum relics. The exile's feelings remain essentially unresolved, implying that a breach now exists for him that is unbridgeable.

Another meditation on change is the long poem 'Am Faigh a' Ghàdhlig Bàs?'/'Shall Gaelic Die?' (1969). Will it die out, cease to be spoken? Is it a suitable medium for expressing every aspect of experience? Smith views language and culture as inherently linked. As he says, 'The Highlander who loses his language loses his world.' Although diversity is celebrated, 'A million colours are better than one colour, if they are different', the poem ends bitterly with a sense of inevitability: ' "Immutable, perfect", Midas with his coat of gold and of death.'

The critical essays collected in Towards the Human (1986) demonstrate Smith's unyielding views on the state of the modern world. He contrasts particularly the urban experience, 'a land where people no longer feel at home' (p.42), with a potential human community, as yet unrealised. He perceives poetry, careful and well-written poetry at least, as a means of telling the truth, of tracing 'those motions of the spirit which see the human being as he is, whoever he is, and really notice him.' (p.56) Thus, an overriding concern is evident in Smith's work with seeing past the dogma and mindless convention to a kind of truth, provided that truth is always open to further questioning and adaptation.