SEO is the work of getting found in search. Content marketing is the work of creating useful material that attracts and persuades customers. They overlap a lot, but they aren't the same thing. Plenty of content is never meant to rank, and plenty of SEO has nothing to do with writing.
Where they overlap
Most pages that rank are content. A guide, a service page, a comparison, a pricing explainer. So the two meet constantly. Good SEO tells you what people search for. Good content gives them a reason to choose you once they arrive.
Where SEO goes beyond content
Technical SEO is about crawling, indexing, speed, redirects and site structure. None of that is writing. Authority comes from links and mentions on other sites. Local SEO depends heavily on your Google Business Profile and reviews.
A brilliant article on a site Google can't crawl properly won't rank. That's an SEO problem, not a content one.
Where content goes beyond SEO
A sales deck, an email sequence, a case study for your sales team, a LinkedIn post, a short video. These are all content marketing. They may never appear in Google, and that's fine. Their job is to build trust or move a deal forward.
The mistake I see most
Treating them as separate departments. One person writes blogs on whatever they like. Another does SEO on pages nobody reads. The blog gets traffic but no leads, and the service pages rank but convince nobody.
The fix is simple to describe. Start from what your buyers search and ask. Write pages that answer those questions properly, with knowledge only you have. Then make sure the site lets Google find and understand them.
Which to invest in first
If your site has technical problems, fix those first, or the content won't get a fair chance. If the site is sound, put effort into your most commercial pages before broad blog topics. Pricing, comparison and "how to choose" pages usually bring better leads than general guides.
See my content marketing and SEO services, or read the content marketing guide.
Written by Aman Potlia.