Lohan, 25, is a former child star with a string of hits behind her such as "The Parent Trap,""Freaky Friday" and "Mean Girls." But her once-bright career has been eclipsed in recent years by legal problems stemming from her addictions to drugs and alcohol.
She went through rehab and is on the comeback trail, having booked a gig as guest host of "Saturday Night Live" in March.
"We're in the middle of casting," Lohan told "Today" show Matt Lauer about her Taylor project in an interview to air Thursday on NBC.
"We start production soon. I've been doing tons of research. But I've always kind of researched her. She's always been a fascinating woman to me. So I'm really honored. And I will not let anyone down, especially myself."
Asked why she felt the need to add that last part to her reply, Lohan said: "I could see where it could be scary for people to invest in me. And I don't want people to have that reason to be scared anymore. So being able to have this opportunity with 'SNL' and the film, I'm gonna do what I'm supposed to do, and enjoy doing it, and do it as best as I can."
Taylor died last year at age 79.
The actress won two Academy Awards and was married eight times.