You may want to have a look at these links: http://onlinelibrary.wiley.com/doi/10.1002/9780470672532.wbepp204/abstract

And the attachment.

Although I do not know of a scale that measures peacefulness, would you consider the construct to be the inverse of aggressiveness? Then scales that assess aggression would be a starting point for examining peacefulness?

You might consider using STAXI-2, an instrument to measure anger. A peaceful person might be hypothesized as one free from anger.

An example of a simple and natural mental technique for eliminating the nervous system dysfunctions that cause anger, restlessness, social opposition, social anxiety, unhappiness, distraction, etc. is Natural Stress Relief (NSR), which is a self-teaching method for learning transcending, which produces deep rest by transcending thinking, feeling, and other mental experiences so that we can experience our true nature, which is pure awareness. The deep rest associated with this procedure dissolves and eliminates the stored stresses resulting from overloads of experience or cognition (see www.nsrusa.org/about-stress.php for details).

The Short Happiness and Affect Research Protocol (MJ Stories et al. 1996) is a measure of subjective sense of wellbeing that you might consider.

Arooj, the answer to your question will largely be determined by: (a) your informed conceptualization of what the peaceful personality construct means; and (b) how this conceptualization relates to things that are important to you (e.g., what you plan to do with this measure). I am unaware of formal measures that focus on peacefulness as a personality construct distinct from other personality constructs, so you may want to start with related measures, take cues from what you think "fits", and, of course, evaluate and validate what you produce (assuming that it is, indeed, the case that no published measurement exists).

It is likely that your conceptualization of what the peaceful personality construct means may include the presence of positive characteristics (e.g., tranquil, harmonious), the absence of negative characteristics (e.g., worrisome), or a mixture of both. You may also want to consider the subjective appraisals associated with peacefulness (e.g., positive and satisfied versus negative and dissatisfied) as well as associated physiological state descriptors (e.g., being calm and relaxed as opposed to being excited or irritated). Further still, you may want to consider the directionality of the peacefulness (ranging from internally-directed, such as being at peace with yourself, to externally directed, such as being at peace with the cosmos). Finally, you may want to consider the possible differences between highly peaceful people and less peaceful people (e.g., do highly peaceful people possess better emotion regulation strategies than people who struggle with peacefulness?).

In the end, my general recommendation is to really crystallize how you view the peaceful personality construct and go from there. In addition to Hansika Kapoor's article by Nelson, I would also recommend that you investigate a few papers on the following topics:

Self-Compassion (http://tinyurl.com/o9n6u4h)

Need for Cognitive Closure (http://tinyurl.com/p23wytl)

Neuroticism (http://tinyurl.com/nv8z64n)

Reading my colleagues, iIcan only suggest an additional thing: the use of case analysis and apply it about one peacefully "personality": Mahatma Gandi.

Consider as an approximation Humility or other facet or subscale of the Five Factor Model of Agreeableness

Hello Arooj,

I think as a first step to measuring or assessing a  "peaceful personality" you should look at definitions of what peace and peaceful mean to the majority of people. If you accept peaceful to be a combination of such traits as tranquil, empathy, altruistic, just, agreeable, humble and so on I agree with Gary that that you use the NEO-PI-3  to assess the full Agreeableness Domain and its six Facets (Trust,  Straightforwardness, Altruism, Modesty (Humility),  Tendermindedness ad Compliance). These Facets all seem very much related to a  person of peace and at peace with him or herself. Agreeableness is taken by Costa & McCrea and others (Widirger) to be the opposite of Antagonism.