diff --git a/nibabel/cmdline/convert.py b/nibabel/cmdline/convert.py
new file mode 100644
index 0000000000..8f1042c71d
--- /dev/null
+++ b/nibabel/cmdline/convert.py
@@ -0,0 +1,66 @@
+#!python
+# emacs: -*- mode: python-mode; py-indent-offset: 4; indent-tabs-mode: nil -*-
+# vi: set ft=python sts=4 ts=4 sw=4 et:
+### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ##
+#
+#   See COPYING file distributed along with the NiBabel package for the
+#   copyright and license terms.
+#
+### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ##
+"""
+Convert neuroimaging file to new parameters
+"""
+
+import argparse
+from pathlib import Path
+import warnings
+
+import nibabel as nib
+
+
+def _get_parser():
+    """Return command-line argument parser."""
+    p = argparse.ArgumentParser(description=__doc__)
+    p.add_argument("infile",
+                   help="Neuroimaging volume to convert")
+    p.add_argument("outfile",
+                   help="Name of output file")
+    p.add_argument("--out-dtype", action="store",
+                   help="On-disk data type; valid argument to numpy.dtype()")
+    p.add_argument("--image-type", action="store",
+                   help="Name of NiBabel image class to create, e.g. Nifti1Image. "
+                        "If specified, will be used prior to setting dtype. If unspecified, "
+                        "a new image like `infile` will be created and converted to a type "
+                        "matching the extension of `outfile`.")
+    p.add_argument("-f", "--force", action="store_true",
+                   help="Overwrite output file if it exists, and ignore warnings if possible")
+    p.add_argument("-V", "--version", action="version", version=f"{p.prog} {nib.__version__}")
+
+    return p
+
+
+def main(args=None):
+    """Main program function."""
+    parser = _get_parser()
+    opts = parser.parse_args(args)
+    orig = nib.load(opts.infile)
+
+    if not opts.force and Path(opts.outfile).exists():
+        raise FileExistsError(f"Output file exists: {opts.outfile}")
+
+    if opts.image_type:
+        klass = getattr(nib, opts.image_type)
+    else:
+        klass = orig.__class__
+
+    out_img = klass.from_image(orig)
+    if opts.out_dtype:
+        try:
+            out_img.set_data_dtype(opts.out_dtype)
+        except Exception as e:
+            if opts.force:
+                warnings.warn(f"Ignoring error: {e!r}")
+            else:
+                raise
+
+    nib.save(out_img, opts.outfile)
diff --git a/nibabel/cmdline/tests/test_convert.py b/nibabel/cmdline/tests/test_convert.py
new file mode 100644
index 0000000000..487bfb7401
--- /dev/null
+++ b/nibabel/cmdline/tests/test_convert.py
@@ -0,0 +1,162 @@
+#!python
+# emacs: -*- mode: python-mode; py-indent-offset: 4; indent-tabs-mode: nil -*-
+# vi: set ft=python sts=4 ts=4 sw=4 et:
+### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ##
+#
+#   See COPYING file distributed along with the NiBabel package for the
+#   copyright and license terms.
+#
+### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ##
+
+import pytest
+
+import numpy as np
+
+import nibabel as nib
+from nibabel.testing import test_data
+from nibabel.cmdline import convert
+
+
+def test_convert_noop(tmp_path):
+    infile = test_data(fname='anatomical.nii')
+    outfile = tmp_path / 'output.nii.gz'
+
+    orig = nib.load(infile)
+    assert not outfile.exists()
+
+    convert.main([str(infile), str(outfile)])
+    assert outfile.is_file()
+
+    converted = nib.load(outfile)
+    assert np.allclose(converted.affine, orig.affine)
+    assert converted.shape == orig.shape
+    assert converted.get_data_dtype() == orig.get_data_dtype()
+
+    infile = test_data(fname='resampled_anat_moved.nii')
+
+    with pytest.raises(FileExistsError):
+        convert.main([str(infile), str(outfile)])
+
+    convert.main([str(infile), str(outfile), '--force'])
+    assert outfile.is_file()
+
+    # Verify that we did overwrite
+    converted2 = nib.load(outfile)
+    assert not (
+        converted2.shape == converted.shape
+        and np.allclose(converted2.affine, converted.affine)
+        and np.allclose(converted2.get_fdata(), converted.get_fdata())
+    )
+
+
+@pytest.mark.parametrize('data_dtype', ('u1', 'i2', 'float32', 'float', 'int64'))
+def test_convert_dtype(tmp_path, data_dtype):
+    infile = test_data(fname='anatomical.nii')
+    outfile = tmp_path / 'output.nii.gz'
+
+    orig = nib.load(infile)
+    assert not outfile.exists()
+
+    # np.dtype() will give us the dtype for the system endianness if that
+    # mismatches the data file, we will fail equality, so get the dtype that
+    # matches the requested precision but in the endianness of the file
+    expected_dtype = np.dtype(data_dtype).newbyteorder(orig.header.endianness)
+
+    convert.main([str(infile), str(outfile), '--out-dtype', data_dtype])
+    assert outfile.is_file()
+
+    converted = nib.load(outfile)
+    assert np.allclose(converted.affine, orig.affine)
+    assert converted.shape == orig.shape
+    assert converted.get_data_dtype() == expected_dtype
+
+
+@pytest.mark.parametrize('ext,img_class', [
+    ('mgh', nib.MGHImage),
+    ('img', nib.Nifti1Pair),
+])
+def test_convert_by_extension(tmp_path, ext, img_class):
+    infile = test_data(fname='anatomical.nii')
+    outfile = tmp_path / f'output.{ext}'
+
+    orig = nib.load(infile)
+    assert not outfile.exists()
+
+    convert.main([str(infile), str(outfile)])
+    assert outfile.is_file()
+
+    converted = nib.load(outfile)
+    assert np.allclose(converted.affine, orig.affine)
+    assert converted.shape == orig.shape
+    assert converted.__class__ == img_class
+
+
+@pytest.mark.parametrize('ext,img_class', [
+    ('mgh', nib.MGHImage),
+    ('img', nib.Nifti1Pair),
+    ('nii', nib.Nifti2Image),
+])
+def test_convert_imgtype(tmp_path, ext, img_class):
+    infile = test_data(fname='anatomical.nii')
+    outfile = tmp_path / f'output.{ext}'
+
+    orig = nib.load(infile)
+    assert not outfile.exists()
+
+    convert.main([str(infile), str(outfile), '--image-type', img_class.__name__])
+    assert outfile.is_file()
+
+    converted = nib.load(outfile)
+    assert np.allclose(converted.affine, orig.affine)
+    assert converted.shape == orig.shape
+    assert converted.__class__ == img_class
+
+
+def test_convert_nifti_int_fail(tmp_path):
+    infile = test_data(fname='anatomical.nii')
+    outfile = tmp_path / f'output.nii'
+
+    orig = nib.load(infile)
+    assert not outfile.exists()
+
+    with pytest.raises(ValueError):
+        convert.main([str(infile), str(outfile), '--out-dtype', 'int'])
+    assert not outfile.exists()
+    
+    with pytest.warns(UserWarning):
+        convert.main([str(infile), str(outfile), '--out-dtype', 'int', '--force'])
+    assert outfile.is_file()
+
+    converted = nib.load(outfile)
+    assert np.allclose(converted.affine, orig.affine)
+    assert converted.shape == orig.shape
+    # Note: '--force' ignores the error, but can't interpret it enough to do
+    # the cast anyway
+    assert converted.get_data_dtype() == orig.get_data_dtype()
+
+
+@pytest.mark.parametrize('orig_dtype,alias,expected_dtype', [
+    ('int64', 'mask', 'uint8'),
+    ('int64', 'compat', 'int32'),
+    ('int64', 'smallest', 'uint8'),
+    ('float64', 'mask', 'uint8'),
+    ('float64', 'compat', 'float32'),
+])
+def test_convert_aliases(tmp_path, orig_dtype, alias, expected_dtype):
+    orig_fname = tmp_path / 'orig.nii'
+    out_fname = tmp_path / 'out.nii'
+
+    arr = np.arange(24).reshape((2, 3, 4))
+    img = nib.Nifti1Image(arr, np.eye(4), dtype=orig_dtype)
+    img.to_filename(orig_fname)
+
+    assert orig_fname.exists()
+    assert not out_fname.exists()
+
+    convert.main([str(orig_fname), str(out_fname), '--out-dtype', alias])
+    assert out_fname.is_file()
+
+    expected_dtype = np.dtype(expected_dtype).newbyteorder(img.header.endianness)
+
+    converted = nib.load(out_fname)
+    assert converted.get_data_dtype() == expected_dtype
diff --git a/nibabel/nifti1.py b/nibabel/nifti1.py
index 91ed8a2903..5be146a89c 100644
--- a/nibabel/nifti1.py
+++ b/nibabel/nifti1.py
@@ -2180,6 +2180,24 @@ def get_data_dtype(self, finalize=False):
         self.set_data_dtype(datatype)  # Clears the alias
         return super().get_data_dtype()
 
+    def to_file_map(self, file_map=None, dtype=None):
+        """ Write image to `file_map` or contained ``self.file_map``
+
+        Parameters
+        ----------
+        file_map : None or mapping, optional
+           files mapping.  If None (default) use object's ``file_map``
+           attribute instead
+        dtype : dtype-like, optional
+           The on-disk data type to coerce the data array.
+        """
+        img_dtype = self.get_data_dtype()
+        self.get_data_dtype(finalize=True)
+        try:
+            super().to_file_map(file_map, dtype)
+        finally:
+            self.set_data_dtype(img_dtype)
+
     def as_reoriented(self, ornt):
         """Apply an orientation change and return a new image
 
diff --git a/setup.cfg b/setup.cfg
index e81b1db10b..4defb7eb14 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -76,6 +76,7 @@ all =
 [options.entry_points]
 console_scripts =
     nib-conform=nibabel.cmdline.conform:main
+    nib-convert=nibabel.cmdline.convert:main
     nib-ls=nibabel.cmdline.ls:main
     nib-dicomfs=nibabel.cmdline.dicomfs:main
     nib-diff=nibabel.cmdline.diff:main