Is there a way to get the result shown in the third axes with just a single ax.text() command? Using expandtabs almost get me there, but the text never aligns properly.

Using two plotting commands doesn't seem like a good practice to me, and you always need to guess the distance between both, which might take some iterations.

fig, axs = plt.subplots(1,3, figsize=(12,4), subplot_kw={'aspect': 1, 'xticks': [], 'yticks':[]})
fig.subplots_adjust(wspace=0.05)values = {'a': 1.35, 'b': 25.1, 'c': 5}tmpl = """Param1: {a:1.1f}
Long param2: {b:1.1f}
Prm3: {c:1.1f}"""mystr = tmpl.format(**values)
axs[0].text(0.1, 0.9, mystr, va='top', transform=axs[0].transAxes)
axs[0].set_title('Default')tmpl = """Param1:\t\t\t{a:1.1f}
Long param2:\t{b:1.1f}
Prm3:\t\t\t{c:1.1f}""".expandtabs()mystr = tmpl.format(**values)
axs[1].text(0.1, 0.9, mystr, va='top', transform=axs[1].transAxes)
axs[1].set_title('Almost there')labels = """Param1:
Long param2:
Prm3:"""tmpl = """{a:1.1f}
{b:1.1f}
{c:1.1f}"""mystr = tmpl.format(**values)
axs[2].text(0.1, 0.9, labels, va='top', transform=axs[2].transAxes)
axs[2].text(0.65, 0.9, mystr, va='top', ha='right', transform=axs[2].transAxes)
axs[2].set_title('Target')

Use a monospaced font so that each character takes the same amount of space.

import matplotlib.pyplot as pltfig, axs = plt.subplots(1,3, figsize=(12,4), subplot_kw={'aspect': 1, 'xticks': [], 'yticks':[]})
fig.subplots_adjust(wspace=0.05)values = {'a': 1.35, 'b': 25.1, 'c': 5}tmpl = """Param1: {a:1.1f}
Long param2: {b:1.1f}
Prm3: {c:1.1f}"""mystr = tmpl.format(**values)
axs[0].text(0.1, 0.9, mystr, va='top', transform=axs[0].transAxes)
axs[0].set_title('Default')mono = {'family' : 'monospace'}textblock = "1234567890\nabcdefghij\nABCDEFGHIJ\n         0"axs[1].text(0.1, 0.9, textblock, va='top', transform=axs[1].transAxes, fontdict=mono)
axs[1].set_title('Monospaced text block')axs[2].text(0.1, 0.9, textblock, va='top', transform=axs[2].transAxes)
axs[2].set_title('Not monospaced')plt.show()