I read the book in the mid-90's and it seemed physically older (10 years at least), though that could have been poor care as well. Paperback with no recall of the cover, but thick-ish in the range of ~500 pages.
Each section (possibly single chapter, or a few chapters) included the place and date on the opening page. In the book, either as an included review or the author's notes, the disjointed timeline is claimed to be in the style of, or influenced by, Celtic traditional story telling. I recall that there was at least one section in the pre-1000 AD range (800s or 900s) and one section was in the 1400s. The time span could be greater than that, but it's at least that wide.
The main character, a male, is a mage, though I don't recall him doing big, or fantastic, magic, just simple things like starting a fire with wet, un-burnable, wood, or causing healing to happen extra fast, but not instantly. The book follows him as he reappears in each time frame - though at first it's not obvious that it is the same guy because his life situation seems different each time. Turns out he is reborn (reincarnated) in each time and has to relearn most things, as opposed to being born knowing how to be a mage, though he seems to have a very limited amount of past-life memory.
The plot, when straightened out in time, is that he has to find some woman (also repeatedly reborn) that he's connected to in some soul-mate type manner (without romance necessarily), and, I think, convince her to also become a mage. With each rebirth his location and hers changes, and part of his problem is just living long enough to find her. I believe that it's a geas he has, and I think, succeeding in getting her to study magic will allow him to stop being reborn, or at least live his life without having to search for her.
I do recall that in at least one section he finds her when she's on her death-bed, thus wasting that lifetime. I don't recall him ever having a high-station in life, though sometimes a very low station. Her, on the other hand, I think had one or two occasions where she was either born high, or married high.