How to set default font family in React Native?

The recommended way is to create your own component, such as MyAppText. MyAppText would be a simple component that renders a Text component using your universal style and can pass through other props, etc.

https://reactnative.dev/docs/text#limited-style-inheritance

There was recently a node module that was made that solves this problem so you don't have to create another component.

https://github.com/Ajackster/react-native-global-props

https://www.npmjs.com/package/react-native-global-props

The documentation states that in your highest order component, import the setCustomText function like so.

import { setCustomText } from 'react-native-global-props';

Then, create the custom styling/props you want for the react-native Text component. In your case, you'd like fontFamily to work on every Text component.

const customTextProps = { 
  style: { 
    fontFamily: yourFont
  }
}

Call the setCustomText function and pass your props/styles into the function.

setCustomText(customTextProps);

And then all react-native Text components will have your declared fontFamily along with any other props/styles you provide.

For React Native 0.56.0+ check if defaultProps is defined first:

Text.defaultProps = Text.defaultProps || {}

Then add:

Text.defaultProps.style =  { fontFamily: 'some_font' }

Add the above in the constructor of the App.js file (or any root component you have).

In order to override the style you can create a style object and spread it then add your additional style (e.g { ...baseStyle, fontSize: 16 })