"I am very excited to share with you guys that William and I got engaged over the weekend," Conrad wrote Sunday on her personal blog.
Conrad, 27, met the 33-year-old Tell on Valentine's Day of last year.
"Just looked at the calendar and realized it was a year and a half ago today that I met this guy...And I sure am glad I did," Conrad captioned an Instagram photo in August.
The designer, author and styler blogger promised to document her wedding planning online.
"I am beyond thrilled! Get ready for lots more wedding content here on LaurenConrad.com as we begin the planning process," she said.
"William and I are overwhelmed by all of your warm wishes. Thank you so much for sharing in this special moment," Conrad added.