To get a handle on Francis’ life, it is important to go into the project with several presuppositions. First, the actual historical data about the man Francis is incomplete and at times maddeningly imprecise. Secondly, objective historians have not, in my view, ever fully connected the biographical facts we do have with the charismatic impact of the man, then and later. Thirdly, it was and is difficult to separate the person of Francis from the order he established; in the medieval mind the “friars” were a gentle pastoral revolution of reform, significantly more holy and effective than the secular clergy. In some sense the reputation of Francis was enhanced by the work of his later followers.
Fourth, the appearance on the scene of two great founders and religious orders (Dominic’s order the other) is one of the half-dozen or so defining events of the Middle Ages; secular historians of the era have thus weighed in heavily on Francis and the friars from a wide range of interests—pacifism, university life, banking practices—where the Order had significant input by preaching and example. But most of all the Franciscans were rent by a major ideological rift whose seeds go back to the very burial of Francis, and each side portrayed a Francis to support its ideological position.
We might call the two sides the conventuals and the zealots. The majority of friars were comfortable making moderate accommodations to Francis’ Rule, allowing for permanent residences (or “convents”), libraries, and less severe austere living accommodations. Their intellectual spokesman was the Church Father St. Bonaventure. We are lucky that a man like Bonaventure held office when he did, being himself a holy friar and well connected in Rome. He wrote what many considered to be the first definitive biography of Francis. Regarding this biography, I wrote in a review in 2005 that
“A pivotal character at this juncture was St. Bonaventure, Minister General of the Order [1257-74] who subtly but permanently established much of what would be recognized today as typically Franciscan. Bonaventure sensed that the friars could not maintain Francis's standard--he had only to open his eyes to see that--but that even the "noble effort" was winning respect from the Catholic populace of Europe. Bonaventure advocated strong clerical identity. The typical friar would be priest, not a lay brother. Bonaventure commissioned an official biography of Francis to reinforce this mainstream vision. Whatever one thinks of Bonaventure, his emphasis upon pastoral ministry, education, and missionary work brought inestimable spiritual riches to the medieval Church.” (From a review of The History of the Franciscan Order, John Moorman.)
Even at the time of Francis’ death, however, a number of friars identified themselves as purists, or as they are known in history today, ‘The Spiritual Franciscans.” The most definitive work at this writing is David Burr’s The Spiritual Franciscans: from Protest to Persecution in the Century after Saint Francis. Spirituals argued for a more austere life. But their interpretations of Francis in their writings were marginal and eventually heretical. Spiritualist writing on Francis is apocalyptic, that the founder was a great prophet ushering in a “Third Age” or the age of the Holy Spirit. Spirituals denied that popes had the right to mitigate aspects of the Franciscan Rule and life; this led to their persecution and eradication by Pope John XXII.
Thus, in selection of a biography of St. Francis, it is good to remember that biographers to the present day bring a variety of agendas to the task (most recently, ecology and global warming.) The best recent biography I have read is Francis of Assisi: A New Biography by Augustine Thompson. This author devotes about half of the work to a narrative of Francis based on what is historically probable. The balance deals with the many early sources and their various critical strengths, shortcomings and agendas. The bibliography of primary and secondary sources is excellent. I found it intriguing and surprising. I have an Amazon review posted.
The best combination of history, analysis, spirituality, and even some whimsy and poetry is Francis of Assisi: a Revolutionary Life by Adrian House. I have a review posted at the Amazon site. I found the work generally free of egregious bias and an enjoyable read. It is probably a good introduction to Francis and his times, and the author does not run away from critical questions.
A good follow-up is the Moorman history of the Order. The Burr book on the Spirituals is specialized but extremely well written, and it too contains an outstanding bibliography of medieval Church life. I should note here that Amazon carries 1300 books under the heading of “Franciscan spirituality.”